You CAN send DrumRack Cells to actual return tracks. When you create a return chain in your drumRack select the return with your reverb on it from the menu under "Audio To" in the I/O section of the drumRack.
ALSO, you can nest a drumRack within a DrumRack cell giving you more routing and macro mapping options if needed.
I do this all the time. My plug of choice is utility, for no other reason but the name really.
Kruddler, You can send 6 return tracks within the drunrack to the main returns:
Start with activating one by droping Utility (or whatever plug) on the first return in the drumrack. Copy the new return track with the plug. Remove the Utility plugs from the two returns. Now copy the second return 4 more times, and you should have 6 in total returns to the master returns.
There needs to be a plug in the returns to create these kinds of returns. But you can remove those plugs when the main returns are selected as i/o for the drumrack returns.