I would think that they should work together. Just be careful with your asterisk version, because there is a bug in more recent asterisk versions that conflicts with chan-sccp. I personally run 2 different systems, one with my main freepbx system, and one that is running asterisk 20, and that one has the sccp driver. the usecallmanager patch should work just fine, but you will have to rename the chan_sip.so file to something like chan_sip1.so, since freepbx will actively target it and disable it.