Some months later he asked the Chief Pilot for feedback on the event.
He was told nothing had been heard back, and that it is common to have no response from the US to such reports.
Why so?
I'm sure your company heard nothing back because the situation you described is perfectly legal in the U.S.; it probably happens a few hundred times per day over here, and it most certainly doesn't always result in an RA every time. The only requirement for such an operation is that traffic info be exchanged.
If procedures were followed, then your report of an RA on the radio should have generated a QAR, (quality assurance review), and the tapes were reviewed in house to insure the controller had 500' and traffic was exchanged. If those conditions existed, no further action was warranted by U.S. regs. Let me stress that a QAR would result from your verbal report of an RA alone.
And, quite frankly, while I'm sure most crews get a bit peeved about having to respond to an RA, I almost never hear a U.S. crew get testy about 500' verticle separation VFR/IFR so long as I issue traffic to avoid a surprise. It's quite common over here.