I'll say first off that she's not worth it, but I would just be too curious to not "meddle" some more and find out exactly what that dude's deal is. (Even though, IMO, the OP wasn't meddling. It was more like exploring--as far as he knew, she was single. . . Or involved in a realationship. . . But a dude needs to find out first before he makes a move.)
The dude (Angry) is a fool for thinking his behavior is acceptable to normal people. And I'm incredibly surprised that anybody is actually coming out and defending his paranoid, irrational behavior. He's checking her phone logs, IM history, probably reading her e-mail, and Vegas Girl is probably not even aware of how little trust Angry has in her. He was obviously in some kind of impulsive rage on the phone, and if an entry in phone log makes him stupid enough to redial the number to yell and cuss at whatever male voice picks up at the other end, I couldn't imagine what a real crisis would cause. Angry is paraniod, impulsive, and potentially violent. It's not normal, much less acceptable. If he hasn't hit that girl yet, it's not a long time coming, IMO.
Women, girlfriends, wives, etc, are not property, and are not there for men to control. (And even if a woman is considered property in your little mind, let me tell you, the above method of "control" actively demonstrates the complete opposite.)