From what I have read about Radeon Chill it sounds like it helps the GPU run cooler by reducing usage in areas it deems not in need of full GPU power. It also only works in a limited number of games at this time. There is a whitelist of DX9 and DX11 games it works in if you search for it. So to answer your question, if a game supports Chill AND Crossfire yes most likely it will work.
one addition to derrickgott007 post. If you are on Windows 10 Anniversary disable the AV (Windows Defender) while you game.
I can get 2-3 fps more with it disabled and higher benchmark numbers. Disable the Prefetch service too, it starts sometimes when I game and it start reading your disks like crazy causing FPS drops even on SSD. And disable the Windows Xbox DVR. Check if you gain something disabling Relive option. (Radeon DVR)
The new Windows 10 Creators has a new "gaming mode", its supposed to stop background services and to give the game more priority. But all reviews didnt find any gain in performance.