When they check if you qualify for Careers profile, do they only take in your history from StackOverflow, or from other computer related stack exchange websites as well?
It depends. There are two options on the request an invite page. If you're choosing to auto qualify with your StackOverflow account, we'll only be looking at your history from StackOverflow. If you choose to request an invitation, we'll follow any link you provide including other computer related Stack Exchange sites.