I guess it's worth looking up. I know if you don't hold your abs in tight when you work them, that they can build out instead of concave. I got that right from a trainer last week, and heard it before from another trainer.
I do not know about losing the fat first, that doesn't seem to make sense to me. I would see no harm in trying to tone up WHILE you lose the weight, just hold your abs in tight when you use that thing.
I am trying to tone up while I lose the weight and now I am starting to see definition in my arms and abs. It is a huge motivator for me.