The updated answer with the release of SE 2.0
With the introduction of Stack Exchange 2.0, associating accounts across the whole Stack Exchange Network is possible and encouraged. There is also now a new central hub for all SE sites, accessible through the Stack Exchange link in the top bar of every site, and by visiting Stack Exchange. Once sites leave Beta from Area 51 they will be added to the footers of appropriately matching sites, and also be highlighted on Stack Exchange.
The following answer applies to SE 1.0 Sites
The answer to both questions would be No. I would assume the link in the footer could be done if they applied to become members of the League of Justice.
CareersOverflow is a Stack Exchange site which is an official fork of the original Stack Overflow codebase. It's not part of the official Stack Overflow Trilogy. Only the trilogy sites and League of Justice members are placed in the footer. Stack Exchange sites are independently owned and maintained and hosted and developed by Fog Creek. The databases are completely separate and there is no way to associate accounts the way it works on the Trilogy. In fact Fog Creek does the hosting for Stack Exchange themselves.
The official trilogy in four parts are:
It is acceptable to suggest to users to ask a question on any website more appropriate to their question if it is not covered by the trilogy, whether it is part of Stack Exchange or not.