My last name is Zabel and I've always been taught that it was pronounced Z-able. Don't know very much about it though, unfortunately not connected with that side of my family.
Zabel sounds a bit like 'sable' to me. Then again, I might not be pronouncing it right! :) I think it's a cool name, over all. It would work well for a foreign princess in some fantasy story. I wouldn't use it for my own kid, however. I think it's a bit too weird for normal use.