Hi! :)
I have a Sapphire Nitro OC+ 6900XT, I put both kexts and SMC after VirtualSMC, but apps with iStats, stats, Eul, none show the temperature (they read from VirtualSMC, right?), but your RadeonGadget app works normally showing the temperature.
I'm using Opencore 0.7.8 and all kexts...