I just bought and ran it (on Windows 10 x64), it ran fine.
It's not using ResidualVM, though it could be using a patched executable.
bgbennyboy had released a launcher
that would do that.
I have the original data that I could compare an MD5/diff against, though I can't find them at the moment. Might do later this week.
EDIT: The IMT files are merged rather than both of them copied like it's described here: http://wiki.residualvm.org/index.php/Da ... key_Island
...so to me it does indeed look like the launcher/installer from above was used. Or at least something along those lines.
I believe that would prevent ResidualVM from running it properly with GOG's data files, for now.
Also, is it me or did something with the license happen? COMI got GOG support just a few months back as well, as well as some SW titles.
Maybe the Mouse is more lenient with licensing for old stuff like this. Someone tell Ron Gilbert and get the ball running on Monkey 3a again