I have always wondered about this and just compared the cage width and pulley play of an xtr m971 and a bottom-of-the-range Tourney I have, I can't tell any significant difference, if anything the xtr's top pulley has a little more side-to-side play.
Since chain inner widths (which determines pulley width profile) aren't any different and cable pull ratios are well known to be identical, I can't see any reason why it wouldn't work perfectly. Certainly no harm should arise by trying, imho.
ps To be sure, I have just checked the late great Sheldon's page and
it confirms as much.