I don't think he is. For starters, in Super Goofy stories, Mickey never appears and the police seems to totally count on Super Goofy's strength rather than on Mickey's genius. In Mickey's stories, Goofy always comes across as somewhat stupid, so that Mickey shines even more by comparison; I don't think that, in that universe, he has a secret superhero identity.
My take is that the Super Goofy stories take place in a no Mickey universe. Mickey either was never born or never interacted with Goofy or O'hara.
Almost a cameo - Mickey drives Clarabelle to the airport in pages 2-3; all the "real" story is only with Clarabelle and Goofy/Super Goofy ("Pete" is also not real Pete).
According to INDUCKS, Super Goof has appeared together with Mickey in 104 stories, as of the writing of this comment. Mickey is most certainly a part of whatever universe Super Goof exists in.