It depends on the couple's dynamic and what they both consent to. As long as Dong Gyun is ok with Jiwon performing sexual acts on him while he's asleep, there isn't a problem. But if Dong Gyun did not consent to it or is VERY against it when it happens, then it's a big no-no. From what we know about these two, they're freaky when it comes to sex and Jiwon was actually very considerate to not penetrate him until he was awake. He was aware of the boundaries and performed within them until he was given the ok to go further.
I think it depends on the type of things you agree on with your partner. Here is just a moment and we don’t have a full story. But if you do something like that to your partner and they’re ok with it, I think it’s fine. DG didn’t seem to mind. Some people actually like to be woken up like that.
On the other hand, if it’s not something you know the other person is comfortable with, you shouldn’t just go for it. Better ask first. Otherwise it can look like rape/molestation.
I think it depends on the level of intimacy, trust and boundaries on a relationship. If they’re both on the same page, it’s fine. Here it’s difficult to evaluate cause they don’t discuss it, but dg didn’t seem to mind.
One question, did you think it was normal for the jiwon to play the dg while he was sleeping? I won't be rude, it's just a genuine question