Well... I got up to some dodgy stuff in my "platonic" male friend's bedroom. And he would totally have done way more with me, if I'd let him. He didn't care that his mom was in the house!
Oh! And there's also that funny story my husband likes to tell of the time he had a girlfriend over at his house. They shut themselves up in his basement bedroom and ... let's just say there was noise, which you could hear if you stood in the right place upstairs. His dad heard them, banged on the floor and shouted, "What are you doing!?"
Well my husband didn't want to admit what he was doing with his girlfriend, so he shouted back, "I'm just playing with Jimmy!" (Jimmy was his best friend.)
Dead silence. Then his dad roars, "That better NOT be Jimmy you got down there!"
So would I trust my kids shut up in a room with someone they might theoretically want to

...? I honestly don't know.
Sorry, I can't be more helpful! My guy instinct, however, is to leave the door open.