I have bought many flights using my AMEX membership rewards points. Everytime i have done it I have received both EQM and RDM. It is not opaque as you can pick your flights and airlines.

One time i ended up on a USair codeshare on UA for the first part and UA for the second part through the system as it was cheaper than anything I could find. Used points got EQM and RDM on all legs. Now checkin was fun, but that is another story.