Only required files on boot partition are uImage, u-boot.img, and MLO. I proved this to myself by removing the other files and successfully booting the 2.6.32 kernel.
Process for building:
bitbake virtual/kernel -c [clean -> configure -> compile -> deploy]
(in the above, -> means "followed by").
2.6.29 and 2.6.31 both seem to brick the device after uncompress of uImage file. No further output in minicom, LEDs D6 and D7 stay solid on (typically, during boot, you will see them flashing somewhat randomly). I'm bummed about not being able to boot either of these (at this point at least) since these kernel versions have RT linux kernel patches available for them.
2.6.32 boots no problem into a command prompt.
2.6.37 looks ok, mostly -- LEDs D6 and D7 flash, but no minicom output. I plugged in an ethernet cable and was able to SSH into the device, so it booted. Perhaps the tty configured for the kernel is bogus? Some searching turns up the following: