Ok, so I was bored and tried to use a different switch's emunand. Causes an immediate power-off, doesn't get to any boot screen (other than the initial SX OS one). Has anyone gotten further than I have?
My notes so far (the names Switch #1 and Switch #3 are for my use, as I have one named Switch #2 that was not used for this experiment):
Switch #1 is on firmware 6.0.1, emunand created with SX OS 2.0.1. I chose to not backup user partition, and 10GB emunand size.
Switch #3 is on firmware 5.1.0, emunand created with SX OS 2.0.1. I chose to not backup user partition, and 10GB emunand size.
I verified that I could boot into emunand with each Switch.
I backed up nand00.bin, nand01.bin, and nand02.bin from both Switches.
I copied Switch #1's nand00.bin, nand01.bin, and nand02.bin files to Switch #3, overwriting the files already there.
I then tried to boot Switch #3 straight into emunand (SX OS does this if it detects emunand is present). Black screen after SX OS screen, appears to have fully powered off (inserting dongle and pressing power button will cause SX OS screen to appear again, so it doesn't appear to be hanging, just powering off). I then went into the SX OS menu (vol+ while pressing power), disabled emunand, was able to boot into CFW. Powered down, went into SX OS menu, left emunand enabled (the default) and tried to boot CFW, powered off as before.
I'm currently recopying the files, just in case something was messed up during that process.
If you have any ideas for me to test, I'm all ears. My guess is that the current emunand implementation does not support running an emunand from a different console. I thought that perhaps TX didn't implement it because of licensing (how would you support two license.dat files, one for the real nand and one for the emunand?), but it seems to be deeper than that.