Well we cant totally discount the lone wolfs and their wiley ways.
I'm not saying that a whole team of them is going to get the job done, but somtimes all it takes is one tricky lone wolf to get the enemy screwed up enough to let the main bulk of the team get through to the next objective.
I think the key is when you find a lone wolf is on your team, find out what he's doing, you just might be able to use his lack of visable teamwork to your advantage.
Or you can allways start talking with him and asking him to help you out with some specific stuff, or try teaming up with him and help him out instead, you might make him feel like he's part of the team or that his playing an important part in the outcome of the game and he may become a little more cooperative in the future.
Sometimes I think many lone wolves are the result of shyness. (Though not all the time, I myself have gone off alone for reasons other than being shy.) And I think the player in question may be feeling nervous about working with a group of people he has never met, maybe he may even fear rejection or making the team lose because of his actions, or whatever the reason is that he acts alone. A few kind words of advice or praise, or even telling that character to "lead the way" may be all they need to losen up a little.