What, *specifically*, makes this mod incompatible with other Atlas creature mods, particular the Animals of Atlas mod?

I am running a heavily modified server where every last spawner is being reworked. There are animals that I prefer in one mod, and others that I prefer from the other -- the ones I don't want will not be spawning at all. (So, there won't be two different copies of the razertooth running around, for example)

If the incompatibility is just "Tigers from Mod A are not the same as Tigers from Mod B" then this isn't an issue, but if there is another underlying problem, like files overwriting one another or something, can I get more information?