If you extract a song from the game (e.g. 000_ROL.dmp), and strip out the non-MIDI data (the ROL header data) using e.g. a hex editor, then use your mid2rol tool, does the resulting file work in a native SCUMM exe?
Maybe the format of the MIDI files is a different version of the file format than whatever the original SCUMM interpreter supports. I assume ScummVM's MIDI handling would be more forgiving/up to date. Just guessing, though.