I dunno if a hill giant would accept being controlled by goblins, at least overtly, but they might be playing wormtongue. I'd think they wouldn't live very long in that grouping. Modern gnolls are basically killmonsters, they have no motivation beyond tearing shit up.
Monsters do have some behavioral info in their text blocks, but it's not always complete and doesn't always jive. Hobgoblins for example, which are also as smart as humans and basically crack military types, highly disciplined and capable of advanced strategy and tactics, throw all that in the trash and just charge in recklessly when they see an elf, for example, which is weird. If I remember right they also misuse goblins, doing the usual "just run forward and melee until you die" tactic with them when they should be smart and tactically adept enough to recognize their real use as skirmishers. Goblins excel at viet cong tactics, kobolds are the classic trap race but there's no reason goblins can't do it too, and their hide on bonus action means they can shoot, vanish, and relocate every round in rough terrain. Just rules-wise they can punch well above their weight when played properly, and in a more narrative context with hobgoblins and goblins fighting a human force, can't discount the morale effects of a force like that. Constant random harassing attacks, poisoned and infectious arrows, booby-traps designed to maim instead of kill, and chasing them into the woods is exactly what they want you to do.
The rules support this, but they're almost never used in this way in published adventures. Despite me going on and on about them I fucking hate goblins and never use them. They're such an absolute known quantity, pose zero threat (unless you use them right in which case they're a very possible TPK), just reek of everything boring and bland about D&D.