Technically; probably, if you want to do all the exporting work. Rigging in unity is different to FPSC; in fact Unity (esp. v3) is just a whole different ballgame, chalk and a large part of the output of Holland spring to mind.
Licence-wise, it will be a very different picture, especially with the third party developers.
Last thing; given what Unity can do, the models and polys it can cope with, using FPSC media, great though it is in its intended engine must be a bit of a backwards leap.
However, you'll have good reasons, so good luck, but watch that licensing very carefully.