Alright, let's say I play Post with Mojoverse face-up. Can I chain his coming into play with Mojoverse, making it so I don't have to stun a Bhood character? (assuming I have no other Bhood characters.)

If there are no Brotherhood characters when Post's effect resolves, then there are no characters to stun.

Yes, I know, what I'm asking is am I allowed to do this.

Yes you are. There are no restrictions on recruiting Post. If his triggered effect can't do anything, then it just can't do anything. The recruit isn't hindered.