First of all, you have quite a bit of drag with a tube. It doesn't glide like a kickboat does.
Next, where are your feet going to be when you start to row? In a kickboat you have the foot pegs to place your feet. With your feet on the pegs, it helps in keeping your body where it belongs. In a float tube, you'll be hanging your legs in the water causing more drag. (Going back to the first problem)
How long are the oars going to be. In order to be more efficient, they have to be the right length.
I would also think that correct placement of the "oarlocks" in relation to where the angler is seated is a big consideration.
I think there are certain reasons that manufacturers haven't put oars or even made strap- on oar assemblies for tubes already. I would think it's been thought of many times buy just about every tube manufacturer out there and just isn't feasible or cost effective.
But if you can make it fly, go for it and good luck.
As for the Zephyr tube, China only? How big is it and is there U. S. dealers?