kronicklez,
Between the MC-LAG peers we'll have the ICCP protocol and the ICL link. You can have them both through the same physical link or in two different physical links.
If you have the ICCP protocol over the ICL link, you don't need RSTP, because the ICL doesn't allow arp/mac learning, then a spanning tree protocol is not required because no loop will be formed.
In the other hand, if you have two Switches as downstream devices, it is recommended to enable RSTP in both MC-AEs and on the downstream device as well.
The MC-LAG peers should be the root bridge
Regards,