I went out and looked at mine, and it seems they are slightly different right where the sprocket attaches. Not sure if this would be a problem, but it "looks" different. I can see splines on the YFZ axle near the sprocket, but none on the Raptor. Like maybe the sprocket carrier piece slides on from the opposite direction. Again, it may not matter on installation.
Edit: Added some pics. Hope that helps a little...
They do not work unless you are skilled at modifying and dont mind trashing some pretty expensive parts. A local guy here put a durablue from a raptor on his, When I asked him to explain what was all involved he started by lapping down the brake hub and adding spacers( I cant remember if it was inthe carrier or at the sprocket hub) but the conversation droned into that subsonic speech that occurs when you've heard too much but are to polite to say enough already. He is a Yamaha dealer so for him it wasn't a big deal but the average guy would't bother after linining them up side by side.
i asked RPM... they are 2 different axles.... save up for the one that fits... it will save a lot of headache.
i keep New RPM axles in stock... i have 1 in for the Raptor, and 2 here for the yfz if you need one