Not exactly. Believing in destiny or fate is believing that things cannot be changed at all, which isn't quite it; at the same time, he definitely does believe that all things - life, the world in general - and not just alchemy adhere to Equivalent Exchange. If something happens, it's because it was caused by another force, even if you aren't necessarily aware of the force itself. It's less that he believes in destiny/fate and more that he believes in some sort of large and overly-complicated butterfly effect.