Yeah, but you still need at least a few to get started.
Not that there is no other way to get the black dye (ink), but they require a bit more work.
From what I know, Vanilla mobs are not the only ones to suffer from Mo Creatures, angry zombies and other mod-added mobs are quite hard to find too.
I would point out that I don't play with Mo Creatures, so I only speak from reading the forums, where people complain about spawn rates of those.