The beautiful face above is the best shot I could get with my rudimentary capture equipment, but it gives me some solid leads. I have narrowed the army composition down to two ideas. Both of these ideas are settled very heavily into Norse mythology, as the armor style matches that of some of Thor and Loki's favorite adversaries from the comics.
First and foremost, this thread from the super bowl commercial has been around for a while, and I think it still carries weight. Essentially it would mean Loki gains his army from a deal with Surtur, which would make since, as Surtur was punished by Odin before hand. Surtur has loaned warriors to Loki before hand as well.
However, these creatures look a little more corpse-y to just be minions of a fire lord. My money is on the Disir, fallen soldiers from Valhalla who fall under the Norse Goddess Hela's control. This would explain their numbers easier than Surtur's fancy hit squad of doom.
And what about the giant sky snake? That is either The Serpent, Odin's long lost brother in his all out rage and hatred form (Which seems unlikely for an Avenger's flick and more likely for a Thor flick honestly), or the more likely of the two, Jormungandr, the World Serpent that will squeeze the world dry.
All in all, I just can't wait for May 4th.