Sorry for the spam, but to clarify/summarize:
- RMS: requires empty VertexGroups, requires curly braces around SkinWeights
- Hive: works with or without empty VertexGroups, requires NO curly braces around SkinWeights.

edit: wth, now model checker is failing to read it
edit 2: MDL files saved with RMS also fail in the model checker. I guess I gotta choose which I want to be compatible with. Or add an option for users to choose.
edit 3: model viewer fails to parse even when empty Vertex Groups are omitted. I guess there's some other reason why it fails.
edit 4: ahhhhhhhhhhhh, I figured it out. Hive model viewer expects skinweights WITHOUT curly braces, that's why I had it that way. RMS expects skinweights WITH curly braces.