This is not a newbie question at all, because there is no standard naming convention. I read the description for the naming of these rigs on athe author's website:
1) Yes, same amp (Mesa Dual Rectifier) and cabinet. The name of the cabinet should be in the Cabinet section of the Rig.
2) O = the amp's orange channel, R = the red channel, and M = Merged Profile (as opposed to Studio Profile)