[@SgtEasy]
Yeah, it's totally okay. Although if you make a universe app, people in that universe will still act while you're away.

The tyranid wouldn't ally with the zerg, because they're objectively superior in every way. The zerg were originally designed by Blizzard when they lost the rights to the 40k universe in the middle of making starcraft, which was originally going to be a warhammer40k game. As such they are, in effect, a nerfed version of the Tyranids from the 40k universe.

It should be fine if you limit their numbers.