Emunand is only a phisical nand image, so you can install devmenu with the cfw loader, than run the emunand with another loader.
To do do this you can't simply swap the launcher.dat, because the GW emunand is stored on the sd with the first sector moved at the end of the nand image.
If you know how to extract the CFW emunand (with dd or some equivalent sw) and reinject it with emunandtool, you can boot it with the GW loader or with Mt one. I did it.
But this is of no use, because GW loader doesn't launch the emunand without the cart, the MT loader does, but doesn't eliminates the cia signature check, so your installed cia (including devmenu) won't work.
It's the same if your sysnand and emunand are linked. You can see the cia while in sysnand but can't load them. The code in the launcher.dat makes the difference.