Coke fines will reduce the pump lifetime, but not probably cavitation. You can check fine at the bottom once per week to make history and try to predicted this kind of event.
Yo could be ok with the foam control, but still suffer upset, check level indication (gamma or neutronics) and also top drum pressure (it usually suffer fluctuation during a foam over)
Leaking of ligther material to the bottom could generate cavitation, how is yours experience with that pump during start up?