i was able to do it, so i'll put in my two cents: art's uboot is not that much faster than the standard one. there are other advantages to having it, but if you are not a developer (and a low level one at that) than you probably won't use or see the extra functionality.
so if you're looking to do it just to shave off some boot time, i wouldn't take the risk...maybe you'll gain a second or so. worst case scenario, however, is that you brick the unit.
also, a word of advice for people doing it...follow the instructions on richard's site for best result (that is, flash his custom kernel then use that to flash the uboot, then drop a regular kernel back in). and when you do this your gp2x may "hang" on some or all of the steps...but everything still installed fine for me, so i have a feeling it's just that the custom flasher doesn't reboot for you, and obviously at some points there's no kernel to go back to.
anyway just be careful.
