Hi,
I'm pretty sure that the operation should be unproblematic. I regularly use 'mv' to rename qtrees just "above" the lun. I do this while the lun is online. The same thing works with changing volume names as well.
While I haven't actually mv'ed a lun into a qtree, as long as it is within the same volume, I wouldn't expect any problems. The lun doesn't lose any of its own characteristics by such moves within the file system. Otherwise all such copy operations using snapmirror would be very problematic.
You could always test it with a volume clone, but I think you're pretty safe. If I had the time, I'd run a quick test, but I think you're good to go.
As always, YMMV, hehe... Good luck.