they are definately compatible. there is a lot of mystery about the OB peacocks. scientists and hobbyists alike have proposed that they come from crossing a Mbuna with a peacock, because the OB gene is present in a lot of mbuna species. this with a difference in their personality also, hobbyists often say that OB peacocks are more aggressive than regular peacocks.
The ones I kept were pretty aggressive and they were with a Johanni too, they can hold themselves well against any Mbuna. so these guys should be fine together.
You need to overstock a mbuna tank to keep the aggression at a minimum, so if those are the only fish you have I suggest you go pick up more. upping the numbers in your aquarium could be as simple as buying the $3.00 assorted african babys available at most LFS. and then slowly over time replacing them with nicer fish. if you don`t mind having impure species or the possibility of cross breeding (this never bothered me) then you can get some nice cheap fish to fill out the stocking.