Rarely, if at all. They are sized similar to the old F-28's and DC-9's rather than the EMB 135/145, Dash 8 and CRJ200's that use the F terminal. I've been on many E170 flights, and all have come in and gone out of A/B/C.

On that topic - A-West is used quite a bit for many domestic trips now. That wasn't the case a few years ago, but the concourse wasn't being well utilized until late afternoon when the intl. departures started to begin. So, more flights have been shifted to better balance out its use throughout the day.