I don't have the cab anymore that had dual spinners, but I ran that one in DOS with the same setup as yours. I think the last version of mame that I had installed on it before I sold it was .37b15??
Anyway, are you running Windows? If so, you have to wait until Windows finishes loading before you plug in the COM2 serial connection, as described in the Optimouse driver docs. I don't know if that helps any....
What exactly is happening? Just no response, or are you getting errors, etc??