I used only 2 pokemon at a Latias raid, left to heal both and rejoined,
In a 10-man pick up group raid.
Of course no one understood what I was doing. It was my L34 alt account, and i had no good mons against Latias except a L36 Dnite (DT/DM) and Ttar (B/C). Of course I got some curious stares from all the randoms sround me.
Guess what? I got 13 balls. Even though my L36 DT/O Dnite, my main Lati@s attacker, was in a gym.
I bet I would have gotten 14 if it was my main account in the same raid.
Answers
At most of the raids I do, folks just stare down an tap tap tap. I'd be surprised if anyone actually noticed that you left and returned, and if they did, they probably assumed it was some tech issue.
A lot of people don't use optimal teams, either because they don't want to waste potions or because they don't have a clue. I've gotten the full individual damage bonus (3 balls) in a 14-person raid because so many trainers were using Blisseys and Aggrons.