MMH5.5 - Heroes of Might and Magic 5.5

shouldn't, but I think you're posting in the wrong place. This is the mod creation section, and you're asking about game mechanics. Durman might delete the message.

There, because in the original game, there are practically no mixed groups of neutral creatures, and if there are, they don't join. Here, the MMH55_Mapmixer.exe utility replaces regular neutral creatures with mixed ones.
It's possible that some other mods have a similar option to replace regular neutrals with mixed ones, but that doesn't matter in this case. Because in other mods, the replacement itself might be implemented differently, and the interaction with diplomacy might also be different.