Are 10 speed cassettes compatible with any 9 speed hubs? I have a chris king iso disc hub and not sure if I can just throw on a 10 speed cassette or not?
Yes. 9 speed hubs can fit any 8,9 or 10 speed cassette. The total width of the cassettes are the same. You can even throw a 7 speed cassette on a 9 speed hub with a 4mm spacer.