How well does this mod work with bob enemies?
Would it be reasonable to add compatibility between those two?

Just installed Bob's enemies and tested, also inspected his code a bit.
Yes, these mods can work together. Both our mods keep the vanilla aliens intact, just adding new aliens, so no conflicts.

The only "concern" is just about the loots. This mod does not have code in dropping any loots, like "small-alien-artifact" or "alien-artifact" from Bob's enemies.

My another mod Schall Alien Loot is responsible for dropping loots.
But there is another set of loots (alien ore 1-3, alien artifact), so I have to think about what to do on what all these mods should drop when installed together.
Some players have requested about support to Bob's Ore and Natural Evolution Enemies mods as well. If you care about the loot drop, you may join that discussion as well.

I was more thinking about adding more variants of Bob's bigger biters as even the levatian causes little to no damage in my last turret wall.

I have another mod Schall Endgame Evolution, if you prefer endgame challenge. It provides category V to category X alien, which are scaled up versions of behemoths. I did not apply the fire/laser immunity to them, because they are already very powerful in my standard.
For example, "Category X spitter" can kill turrets, player in power armor MK3 (with any number of shields), and even medium tank MK3 (w/ several vehicle shield MK3) in one shot!

I am not sure about Bob's armor or warfare though, so maybe these aliens don't have enough threat to your Bob's defense.

I'll grab that.
Right now I can stand in an alien nest forever with my mk5 suit and mk5 shields. Don't think they can kill me.