Assuming she isn't really a truck driver from Arkansas called Billy Bob, it might work, it might not same as meeting someone at a bus stop, a pub, a school.
The first question I'd ask myself [rhetorically that is - it's none of my business for the actual people involved here] is why they don't have a relationship IRL with someone on the next block / at the same college or whatever? There are plenty of good answers, of course, but I'd ask myself that - why meet someone on the internet rather than face to face... and not only meet them [which is like "Hey Sharon, fancy a pint / game of tennis next week, a few of us from the blah blah site are going?"] but get to the point where they are talking as though they're in a relationship before they've met?
So, if you'd said "My mate has met someone on the internet, they have a laugh and a joke, she lives 200 miles away, should they meet up and have a date?" I'd think it stood a better chance than the idea I get from your post that your friend believes himself to be in some kind of relationship already. The advice would just be "meet somewhere public, tell someone where you're going" blah blah.
Remember, on the internet no one can punch you in the face, see your reactions, know who you really are etc whilst at the same time it's easier to be open when discussing things that people generally don't IRL unless they are very good friends or more - see the catch? Even excluding the outright dishonest / malicious stuff that goes on and the white lies about their looks / skills / beliefs "Yeah I love status quo too!", the chances are the environment may have changed the way the people behave even if they are honest, and thus your friend or the girl may care an awful lot for someone who isn't going to be the person they meet.
So my advice would be to meet as friends, perhaps with other friends and see where it goes, if anywhere.
As for the 200 mile thing, for a IRL relationship I'd say it was ultimately doomed [people generally form relationships to share their lives / free time, for intimacy and ultimately because women are warm and cuddly] 200 miles away for a protracted length of time and it's difficult to see which of those aspects of a relationship you can have, especially if you don't have a relationship to begin with. Moreso if there's not already a long term relationship / commitment there where the 2 people have planned the time apart knowing each other and knowing at some future point it will cease.
If the people don't know each other and if they are at a stage where they are making many decisions about where they are going to live, what they are going to do with their lives etc I'd say the 2 of them should think very hard about whether "sacrifices" the other makes to be with them might be selfish if they let them. Sometimes caring for someone means telling them to go and do what they were going to do all along, rather than letting them chuck something in to be with you. Especially if the relationship doesn't work out and that old devil called resentment rears its head. After all, that sacrifice / compromise they might be about to do was probably one of the things that you liked about them in the first place.
But for a internet relationship it'll be the same I guess, so your friend will have exactly what he thinks he has now - if that's a relationship, go for it.