The fact that they're not exactly screaming about this violation probably says a lot.
If they didn't care then I would have expected MCC to ask for a non GPL licensed version of the code so that they didn't have to provide source. If they'd done that then I'd have expected MCC to shout loudly that they had permission.
I'm not sure why Dennis wouldn't enforce the license, the FSF will usually help out. Faced with the prospect of a lawsuit then most people just release the source.
The biggest failing of the MCC is that they didn't open source everything & made it easy for anyone to develop for it, I would have bought one if they had.