I like that idea! The whole recruitment process could be full of action and fun times. Or lots of eye rolling from Julio when he realizes that yep, the dude blasting Gaga is actually part of a hero squad.
I really don't see an issue with Mark being the type of guy to make Julio question himself. He's pretty flirtatious by nature so it leaves it open to a lot of moments where his words or actions could make Julio think otherwise. But truthfully if he caught wind of how Julio was feeling, he'd try to be supportive. He'd spam him with a ton of songs for the occasion but he'd definitely be supportive. Maybe something happened between them when they were in school together and it kinda always left a what if between them?