I would expect so given that the Sonic 3D Blast "director's cut" romhack looked like they may have been building it on top of a source code backup instead of hex-editing or reverse engineering.

Personally, I feel like it's not too fair to hold that against a known developer where this stuff is attached to their real life identity. I've always thought that if I ever did indie game dev that I'd make part of the contract that everything would go open source etc after say a decade. That said, especially for licensed games built by a company instead of one guy solo, the reality of contracts and legality isn't that cut and dry.

Maybe someday they'll end up on the open web, but even if they do I'd be shocked if a dev just went "I'm dumping all my dev copies/content publicly with my real name! Come at me lawyers, I ain't scared!".