Why would it be more problematic or require tighter limits? After all, if it's alien, there's more room for it to go nuts and still be alien. If anything, it's the known stuff that requires those limits, or they'll look… well… alien: because they go too far outside what we think of as “known” design.
Then it probably does its job — it's not meant to be alien. It just illustrates how you can create variety algorithmically, and in fact, since it's fractal-based, huge variety is not even part of intended end result — it just happens anyway.
I don't think anyone is really talking about creating lifeforms, but even if we did, there are already plenty of games that do just that and do it really well. Slap a simple decision bot onto a game like Spore or Impossible Creatures or, hell, just rip off NMS, and you're good to go. Sure, for your “hero races” (not in the sense of being heroic, but in the movie-making sense of being the ones that you really show off), you probably want to have a higher level of control — put them higher up in the component hierarchy, if you like — but that's no different than you'd want with the human characters. That's because you're trying to achieve a completely different goal: you're not trying to create variety and new strangeness to discover, but rather offering up a well-controlled other party to interact with, which obviously has other requirements to guide the design.
