I don't know if you, like me, add an extra mixer to your 'main' mixer and then turn around the instruments via the tab button and draw cables between each drum on ReDrum to the extra mixer. If you do this, you just add a reverb to the extra mixer and turn up the knob at the top of the channel on the extra mixer where the drum is. If you don't, add a reverb to the main mixer and then turn up the 's-1' button on the ReDrum machine on the drum you wish to put reverb.
I hope you understand me, otherwise let me know...