For one contract, I'm supposed to recover someone stuck in orbit. I've done it with the grabbing arm but I want to know if it's possible to get the lost guy to board a ship with an empty seat. Tried to sync orbits and take control of him but game doesn't let you do that. There doesn't seem to be any right-click options concerning it either. Any help appreciated.
Yes, you are able to do this. The most important thing to know is that you have to get your ship within ~2.5km in order for the stranded Kerbal to load. Once that's happened, you can switch over to him using [ or ]. After that, it's a simple matter of guiding the Kerbal to your rescue ship and returning to the surface successfully. No right click needed, or anything like that.