I've received MQMs, though that was just before the SM/WP merger, so was using NW #. Shows up in my SM account now, though, with both MQM and RDM.

From the DL web site for YX:

Mileage may be earned on all Midwest-operated flights. Earn 100% of actual miles flown (500 minimum). Earn 100% Medallion Qualifying Miles for fare classes: Y, B, H, V, Q, K, W, M, T, R. O. P. Earn Medallion Qualifying Segments for fare classes: Y, B, H, V, Q, K, W, M, T, R, O, P.

So Midwest-operated only--no Frontier