Flying a VFR transition through the San Francisco Class B (which for all practical purposes means you are flying under IFR, as far as interactions with ATC are concerned) a while back, I was visual with an airliner and he called to say he had an RA (which was obviously me). He sounded annoyed but didn't change course - there was no risk since he was at my 11 o'clock and flying to my left, and climbing fast. I don't know how an RA works when one of the aircraft isn't TCAS equipped (I just have Mode S).
n5296s