You can use the rotors for sure. The adapters are the same profile, but sometimes calipers are shaped a little different and hit the adapter when tightened down. Give it a try, if it doesn't fit right, adapters are all of like 5 bucks.
I just made the same switch...
I am almost rid of Hayes brakes forever and I couldn't begin to tell you how happy I am.
The Formula calipers bolted right onto my Avid adapters and work with my Hayes front and magura rear rotor. Good enough until my Formula rotors show up... they're just so purty!