I've done it both ways, Skyping/video conferencing in to an existing group and having a player skyped into my group. I've also done entirely skype games, as many of my company's employees are international.
Does it work? Sure. Does it work really well? Not in my experience.
The biggest logistical issue is the lag for most video conferencing software, especially the free kind. Even with a good, max-speed connection on Skype, there's a 1-4 second delay with video and audio. If you're trying to have a lively conversation with the skyped player, everyone will have to speak and then wait for him to receive the audio, and then speak, and then for the group to receive the audio.
If you use a paid-for service, such as GoTo Meeting, the delay will be much less noticeable. I already pay for it for my business, and it is very valuable and overall good service, but is not inexpensive.
Whoever is the player that is outside of the group skyping in should have either one of the other players or the GM to do their character's rolls, or use a dice-roller app that the GM can see. Again, this slows everything down a little bit, but isn't bad. I successfully ran a game like this for about six months, and other than the nuisance of the poor quality audio/video, it worked out okay.
Overall, if it detracts from the experience from everyone, it might be wisest to just let the player wait until he can come back for a vacation. Good luck, and have fun.