So long as you don't spawn more then you should be able to of equipment it doesn't trigger the cheater flag, in my experimenting the only thing that raises the cheater flag is spawning too many ammo bags, ecms med kits or c4. Topping up your ammo through the unlimited ammo works without flagging you. Also the red name and cheater flag only lasts for that heist.
So, guys, can anyone confirm that other stuff in co-op like unlimited health/ammo is fine? As long as you don't mess with too many equipments, that is. It seems that it's pretty much confirmed they can't ban you if you you're not flagged by another user, but the red "cheater" thing, if it's permanent, is a troublesome. Another thing, i think everyone here should be (kinda) careful about pd2stats.com/ , although the site says things can be buggy, if someone sees you got the skill tree maxed out, you could be reported. Setting Steam profile to private or friends-only avoids that from happening, of course.