In World War 1 and 2, military forces frequently would not fire upon medical personnel as just a rule of honor. But the aliens have no such honor. If you want medics, they are going to need to be the toughest of the tough. I'd make them fully combat ready, and just have them focus on mobility and capacity to carry supplies around. They should perhaps be a generalized support/combat unit capable of several roles, medic being one of them.
Just tossing ideas.