If Liz Michael is right Mo's plan has worked beautifully.
I'm not even sure that it's the Nation of Islam itself, rather than this Nation of Gods and Earths, or some other such group, or even simply a general call for violence among black separatists.
It seems the goal would be to get the message out clearly to the true believers, but to couch it in language obscure to mainstream America.
However, I still don't see why they stopped hiding and essentially let themselves get caught. Ordinarily I'd say that there might be no reason, just a mistake on their part or emotional exhaustion. But the "duck in a noose" message right before they were captured strongly suggests that they let themselves get caught on purpose.
I think you nailed it.