getting back to the original. . .
How are non-18s treated by 18A? we are talking CPT anf LTs. Well, first they are treated like professionals. The Chem guy and the Sig guys and the MI guys and the AG guys (That might be the exception. Don't get me going on gender-incorrect branch choices) are all treated as deserved by the level of proficiency they bring to the Group -- They wouldn't be there if we could (or wanted to) do it ourselves. Lots of those guys go SF because they are in close proximity and say to themselves (I SO wish I could spell decide -- omg I CAN!

) Anyway, they hang with us and decide "I can do that." AND that is very COOL!

Aside from that they are treated as friends if they are friendly and like jerks if that is what they are. In 5th Group one of the coolest guys was a 2LT Chem officer. (He had lots to overcome and did!)
As for assessing through CA. NAH! It's sort of the other way around. Some awesome CA officers are awesome because they were SF. CA is about exploiting Cultural awareness, SF invented it!
Do what you want.
Just do it spectacularly well. Then bring that experience to being an 18. Infantry is obvious but Tankers, FA, Sig (Col Rowe was SC) bring a different but valuable set of tools. The Finance Officer for 5th Group was in my class, and he was a Great SF Soldier and Oofficer. I got this straight from his Team Sergeant (MSG Max Perdiem), His Team lived Goooooooood!