I was using supplements which contained creatine last year but my raynauds started prior to using such pre-training supplements. I was going to the gym and/or running pretty much everyday though. Obviously since learning of ASS I have ceased using the supplements and cut back at the gym a fair bit. When my Rheumatologist told me I had 'a funny marker' (Jo-1) and muscle inflammation he suggested the Jo-1 was a 'red herring' and the muscle inflammation from exercising prior to the blood test. Before my next blood test I have to take a few days off from exercise.
Creatine, from my understanding, is quite safe and has been used with the elderly to assist with muscle strength. I'm sure I've read about its use with myositis sufferers as well.