Healers are, quiet often, Marines.

A Mage can't be a Marine. They're usually using their warrens during battle, and are protected by the Marines/Heavies around them.

However, if you would like to be a Marine with a lesser unrefined warren, meaning some small skill or talent, that's fine. Some affinity to a warren you were born with, but haven't mastered since you're more of a physical attribute soldier. So no offensive Battlemage powers. I wouldn't want anyone slashing enemies with one sword and devouring them with ice/flames with his warrens.