Unfortunately OP, there's a whole bunch of important information that we're not party to. Was the guy drunk as well. Was he in a relationship? Was she happy in the relationship she was already in, or was she unhappy with her boyfriend? This is the sort of stuff that pushes guys and girls into cheating.
Now, regarding the situation as I see it with the info you've given: the guy isn't exactly a gentleman or a saint. But the woman explicitly asked if he had a condom. That right there is an invitation for sex. Not only did she not turn down his advances earlier, she asked if he had protection with him. If she didn't want to have sex, then ultimately she could and would have said 'No' at any point earlier in the night.
Where I'd give the guy some flak is that he didn't use a condom. That's just not cool. That's the sort of mistake you make when you're a teenager: ie, young and stupid. As an adult, he should know better than that. If it's not someone you're in a steady relationship with, then wrap it up in a raincoat. Simple as.
Lastly, I'm speaking as a guy who has slept with girls in relationships before. And therefore, my last point would be: whatever went on, it's none of your business. To me, it reads as two adults deciding to fuck. Regardless of how drunk they were, whether they were in a relationship, if the dude wasn't exactly a gentleman, it's their private business. If the girl comes to you because it turns out he was a douchebag, then fine, get involved and tell her what you think. But at the moment, yor post reads as like you don't approve of what they decided to do, so therefore you're going to talk dissaprovingly about it.
People fuck everyday. A lot of the time, it isn't romantic, or lovely. A lot of the time, it's simply two people getting drunk and getting physical with each other. Sometimes it's just stress relief. No matter what it is, as long as it was consensual (which you imply that it was), then there's no call for you to go round dissaproving what your friend does. This is the 21st Century. Don't turn into your friend's chastity belt. They went out of style hundreds of years ago.