Well, since The Dig is having some issues and won't play in Windows through Steam (@lucasartsgames says it's "looking into Dig issues") we went with LOOM. Another brief, $5 download later and it works ... in Steam at least. Our attempts to get it to run in ScummVM weren't as successful, despite having all the necessary files available to us, unencrypted. So we went digging, and came up with this blog post by ScummVM team co-leader Sev who writes, "As of the ScummVM compatibility, we see that here were some changes that make the games incompatible with the current ScummVM version."
So, did LucasArts intentionally change the files to break compatibility with ScummVM? Doesn't sound likely. Sev calls the changes "very trivial" and says they "do not seem to constitute any kind of copy protection." Since this isn't any kind of copy protection or encryption, patching ScummVM to work with these new releases would be a "five minutes hack." However, much to our surprise, he and his team have "decided to abstain from it at least for now." He writes, "We do not want to interfere with their sales and/or any upcoming plans for other platforms. Also we are really open for cooperation in this regard and will be more than happy to make any upcoming releases run with use of ScummVM."
Sounds like an honorable stance to us, though one that will deprive this blogger of the ability to play these two games anywhere but Windows. We've reached out to LucasArts for a comment on the format changes and their thoughts on ScummVM enabling playback of these games.