CAE might eat diatoms too and i also have a bristllenose pleco that will eat it but since his problem is on the gravel i don't think they would help much.
I have a BN pleco in a tank with various other algae eaters(SAE,otos,Zebra snail,algae shrimp) but nothign was helping to keep the gravel from getting algae on it.They cleaned the algae form everythign else in the tank but i have never seen them clean the gravel. I got MTS and the problem started going away.