1. valtívar  literally means"gods of the battle-slain", and occurs only here and in Völuspá (52, 63), as the conflagration of the world, Ragnarök, unfolds

[I suggest that the term val-  is used to liken the sacrifical victim to the sacrifice of a warrior in battle. A similar useage is found of the boar Sæhrimnir in Grímnismál 18].

2. námu veiðar is an ambiguous phrase, which occurs only here. The feminine noun veiðr can mean either "chase, hunt" (thus Völundarkviða 4, 8) or "prey, kill, game" (thus Reginsmál prose: sýndu veiði sína). Subsequently, three meanings seem equally possible: "went hunting, were hunting", "made a kill during hunting, caught game", or "feasted off game".

3. sumblsamir - The word sumbl can mean either "drinking feast" or the "drink, ale" itself.

In symbolic terms, sacrifical blood and beer are identical, cp. Fafnismál 14, hjörlegi, 'sword-liquor'. Lögr, dative legi, [English lager] properly means sea, but is also used of intoxicating drink and blood. Mythologically, the poetic mead is made from Kvasir's blood. The sea too is made from Ymir's blood. In the same vein, Thor drinks from the sea through a drinking horn at Utgard-Loki's. The point of the poem Hymiskviða is to obtain a cauldron large enough to brew beer for all the gods. This kettle is obtained by Thor, who carries it on his head [cauldron = head/skull] as he crosses the sea. The kettle ends up in the possession of Ægir, the sea-god, who uses it to brew beer for the gods at their sacrifical feasts [cauldron = sea]. For the same reason, we find skulls used as drinking vessels in some mythic situations.

The reason that Odin invokes "Ull and all the gods" is moot.  Ull may have had a special place in the sacrifical process.

 Atlakviða 30 informs us that oaths are sworn on Ull’s ring (among other things). This practice is best described in Landnámabók (Hauksbók 268).  There, the ring needed to be at least two ounces or more and reddened by blood of the sacrificial animal. It was to be worn by the hof-goði at all assemblies,   and when not in use it would lay on the stalli.  Every man who had a case in the Thing was required to swear an oath on this ring and name two witnesses. The oath was worded thus: "I name [the two witnesses] witnesses herein, that I take an oath on the ring, a lawful oath, ---so help me Frey and Njörd and the Almighty Ás, as I shall pursue (or defend) this suit, or bear witness, or give verdict or judgment, according to what I know to be most right and true and in accordance with the law." An account in Víga-Glúms Saga agrees  with this very closely. There, the man was required to take the oath on a silver ring of not less than three ounces which had been dipped in the blood of an ox.   In Eyrbyggja Saga the oath ring is described as silver, and weighing 20 ounces. During feasts, the goði wore it on his arm. In a description of Thórólf's hof in Iceland, the ring is described as being 2 ounces, and worn on the finger of the goði at all assemblies. The Anglo-Saxon Chronicle gives an example of an oath ring being used by the Danes in 876.

 Besides this, Ull in particular may be invoked in Grímnismál 42 because of his association with the hunt.  As Sif's son, he can be seen as a fertility god, and provider of food. His mother's hair, shorn by Loki, is often equated to fields of grain. Ull is the god of snow-shoes and the bow and arrow (Gylfaginning 31), the same equipment used by the three elven brothers in Völundarkviða to hunt bear to eat.  Ull is most likely of the same clan ( i.e. the alfr,  see Grímnismál 5). His home is said to lie between Thor's estate and Alfheim, the land of the elves.  In Hymiskvida 7, Thor drives his goats a day's distance and arrives "at Egil's", where he leaves his goat-drawn chariot behind and spends the night "at rest" before heading into Jötunheim on foot. Egil is a brother of the elf-prince Völund in the Eddic poem Völundarkviða. While often classified as a heroic poem, Völundarkviða is actually placed with the Thor poems in the Codex Regius collection falling between Thrymskviða and Alvísmál.

From the context of Hymiskvida, it becomes clear that Egil's house is the same place Thor obtains his servants Thjalfi and Röskva, when young Thjalfi is tricked into breaking one of the bones of the goat's leg in order to suck out the marrow (Hymiskviða 37, 38). The full tale is told in Gylfaginning 44:

Ull's stepfather, Thor wields the hammer used to hallow brides, to crush the heads of giants (symbolically likened to "calves", Þórsdrápa 19/1-4), and to resurrect his goats, which can be slaughtered and eaten when he travels. In ritual sacrifice, the victim is commonly struck on the head with a blunt object, such as a hammer, before being drained of its blood and beheaded.  The cattle skulls found at the Hofstaðir site bear evidence of blunt force trauma to their foreheads (see Grímnismal 40-41).  Mythologically, Thor's hammer performs the same function. Raising his hammer, Thor brings death to the sacrical victim, and  simultaneously strengthens or returns life with the same gesture.

Each sacrifice is seen as a reenactment of the sacrifice of Ymir, renewing and strengthening the gods and the world they protect. In a very real sense, the food obtained from the ritual slaughter of animals (and to some extent the ritual harvesting of plants) physically strengthens and sustains the human body. On the cosmic level, the world itself is seen as a human body, having been created from the corpse of Ymir, the first anthropomorphic being. The lifting off of the cauldron (hefja af hvera) might be an allusion to the decapitation of the sacrifical victim, as the head, the breweing cauldron, the beer-cup, and the hlaut-bowl used to catch the blood of the victim are all interchangeable in symbolic parlance. [See The Symbolism of Sacrifice for further examples].