Can you equip the CM-O/93 and take a Mark II Medium Blaster on the same unit?

The Mark II Medium Blaster is its own unit. It has no effect on the Rebel Veteran's unit, so would not effect which upgrades it can take. The unit of Vets is essentially "blind" as to whether or not you are taking a Mark II. The only way in which they interact is due to the Detachment rule, the entirety of which has been in the RRG for some time.