Second, is it possible to have that FXS port call out when it receives a routed call from the hunt group?
Yes, an FXS module/port can be included in the hunt group, in the same way as the BRI modules. If the SEARCH is PRIMARY for all of the entries, then the order they are listed in the DIAL PLAN is the order of the hunt. To change this, you can set the SEARCH to SECONDARY and PRIMARY entries will be used first, and if they are unavailable, it will then go to the SECONDARY matches.
The only way to have the FXS port dial out, would be to have it physically connected to an FXO port (which will be a NETWORK TERM entry), and configure the TRUNK NUMBER as the number you want it to dial when it receives the ring voltage (from the FXS port). If it is to call back out the PSTN, then you also have to disable "Automatic Route Back Rejection" under the DIAL PLAN and GLOBAL PARAMETERS.
Hope this helps,