Mantises are generally fine with corals. Deeper water mantises can develop a potentially dealdy shell disease from high light, but there are a few intertidal species such as P. ciliata and N. wennerae which can take it. Also, if one provides alot of shade then you may be able to keep peacocks (a deeper water species) under metal halides. Smaller mantises such as N. wennerae *may* not bother clams but I believe O. scyllarus will.
Dan