I am thinking about buying a second hand AlienBee 800. I currently have a pair of Yongnuo YN-622C Wireless TTL Flash Triggers for Canon. Would they be compatible with the AlienBee?
You can, using the sync port on the Yongnuo trigger. However, AlienBees use a 3.5mm mono sync, so you'll need a cord that can connect the two up. Fortunately, they exist and Paul Buff sells them. You can probably also find smaller cables, but you may want to consider the long ones anyways as they may let you do some funky strobe positioning, behind things that might block the radio signal.
As a note, if the AB800 you get has the complete shipping kit, it will include this cable. It's used, though, so may have long since been lost. You never know.