A properly acclimatized pleco should do fine. I doubt the cichlids will even notice the pleco. They are armored for a reason. I have kept plecos(Bushy nose, veil, clown, zebra) many times over the years with African cichlids both Mbuna and Tropheus. If you are getting them local you should not have any water issues between the LFS and the tank. I think our domestic fish are less influenced by water parameters than wild caught, I have a discus breeder here who breeds his discus in 8.3 PH hard water, if that says anything. I would say go for it. Although I also urge you to add some herbivore cichlids to the mix, there are plenty of them. I loved my tropheus colony, never had any algae, those little hyperactive buggers scoured the rocks daily(dont recommend tropheus BTW, just saying).