Yes as long as it's not for too long. If it's for the first few weeks of dating when nothing is serious yet, just casually getting to know each other I think it's fine. But once feelings develop you should pick one. Don't date two for months and have them both thinking you're their girlfriend cuz that would likely hurt feelings.
I wouldn't worry about it... they are most likely seeing multiple women too..
As long as they know. If I were one of the guys, i'd be gone pretty fast though, lol. Not because I think it's bad, but because that 'hanging out going on dates no intimacy' stage is not one i'd want to sit in. I'd want to move forward, or move on.
I say yes, but- you should tell them. I recently found out a guy I was seeing (not exclusively but we had intimate moments and I slept over at his house a few times) had been seeing other women and it was a deal breaker for me. Totally turned me off and painted him differently. I don't know, I know many are okay with it, but I refuse to be anyone's part time.