I still will follow RA guidance in the situation you give, even if previously told of the impending traffic.
ANd that's exactly the right thing to do because as you said there could be a hundred reasons for this "resolved situation" in the controller's mind to turn into a loss of separation.
As an example, the latest RA I had was this situation where normally an aircraft was descending to level 110 and the other one (not on my freq) cleared to climb to FL100. The trouble was that the pilot ( american) was climbing to 10 000 feet on the QNH, which was pretty high that day:1028 or something. And as this plane was on another frequency I had absolutely no way to know or even have a clue of what was happening, so when I heard this "TCas Climb" I was surprised, maybe shocked ...but happy afterwards that the pilot followed his Tcas.
And however we have to remind that Tcas is not meant to provide separation (the way controllers see it, i mean like 3NM or 1000 ft) but to prevent collision. And the Uberlingen accident should have taugh that: whether you're pilot or a controller don't ever argue with Tcas !
I think that the problem of this Tcas awareness for controllers is linked to the very short term action of Tcas, which doesn't really leave time to the pilot to advise ATC of the RA. In fact when a pilot hears a resolution is merely 30 seconds away from collision, so definitely his priority is to take action and sorry to say that but not to advise ATC. That's where, as someone has already said, a special and automatic squawk could be useful but then, still you would depend on the speed of your radar...
One last thing, to those who have read the report from Uberlingen, one thing I noticed is the that the Tupolev crew is five . Can you imagine the troubles of CRM between five ? and it might have played a minor role in this... This said, I don't want to blame the crew for the tragedy or to disculp the controller, they've already paid a hard price for what happened.
May they all rest in peace.