My view is that if the heat treatment is carried out correctly during the refurb and powdercoating process then it is highly unlikely that you will experience a wheel failure.
I have provided this service for a number of years now and have probably turned out circa 120 sets of wheels and not had one failure.
I have also done around a dozen sets of GT4 rims with no issues.
My own 6 sets of rays that I run on my track car have also been powdercoated and again to date, no issues.
So to summarise, I believe that if the PC process is done correctly then all will be good.
Alex