MMH5.5 - Heroes of Might and Magic 5.5

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.
Perhaps, some other mods may 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 may be implemented differently, and the interaction with diplomacy may also be different.