To answer your questions, at least the way I would play it...
OCEAN WUN ZERO
Err, I quite often provide RIS and approach services to different A/C at the same time. I don't see how you can have a problem with this?
As Bookworm said, technically when providing an APP/APR service, ALL IFR A/C are to be seperated, even though they are in class G.
Realisticaly however, if the two A/C were transiting under RIS I would only give traffic. If they looked like they were going to get as close as you said, I would give them traffic again and might (at my risk) suggest avoiding action.
If however one or both A/C were inbound, then I would seperate them.
Clear as mud eh? Good point matspart3 - what would happen if there was an accident?