Funny, I was think the opposite: Will my Hobie branded harness work for kite boarding? It's the convertible model where the shoulder straps can be removed, which I would do if kite boarding with it since those are not featured on any of the kite boarding harness I've seen.
Can anyone say if it would be a suitable substitute?
A kite surfing harness like the one I pictured in the first post is designed for kite surfing/traction sports, therefore the spreader bar is built with the massive load on the hook (doubled steel loop, unlike the trap harnesses with a single tang) and directon of pull in mind; pull is almost strait up. I'm sure a trap harness will hold your hanging weight on most flat, calm kiting sessions but I don't know if I'd trust the spreader bar build or the harness stitching to hold me 30 feet in the air after a boost and the forces created by the kite in a boost (Think about a 200lb person being yanked up while accellerating, held by the hook). Also, as far as comfort, the upward pull of a kite presses the spreader bar up and in under your ribs so you want really good padding under the spreader bar which a good kite harness usually comes with. You can probably get away with using your trap harness, but you can get a decent kite harness for about $100 with a spreader, about half for a used one and the used ones are often cherry. If your'e looking for used one, you can check the "for sale" section of http://www.powerkiteforum.com
Edit: The double loop hook on a Kite Harness is for strength but also for locking in to a kite's harness attachement point called a chicken loop (like a trap ring) and a "donkey dick" which goes thru the hook to lock. For trapping, the loop on the harness should not present a problem getting out of unless you use the old style dog bone trap loop. The large trap loops should work fine because they are actually bigger than the kite chicken loop.