I'd let it Reflect things that are Reflectable. Very zen-like, I know. FFT summons ignore Reflect in both FFT and against other systems, and as it happens (presuming the Reflect-Null skill is legal by Floor 4) FF9 summons also ignore reflect. But in a system with reflectable summons, well, I'd let Reflect Mail reflect 'em. But not unreflectable summons. Deep.