This should be possible. Dreambox games are WASM, so anything that compiles to WASM should work.
You'd probably use Emscripten to compile your C++ into WASM, and then use some other utility to build the ISO disc image (only real requirement is it's in ISO-9660 format with a "main.wasm" located in the root directory).
You can view a list of all of the functions you can import here, in the VM's constructor it links all of the functions that are exposed.
The answer is.... I'm not sure, probably not at least for now. Frankly it's very tough to spend any time on this project lately - I've been extremely busy with trying to look for a job, working on my game, and trying to find ways to keep a roof over my head in the meantime. All things considered Dreambox doesn't exactly pay the bills, which makes it hard to justify spending much time on it right now.
