To sum it all up. A mid-dash OD isn't possible. Mid dash, Johnny is in the air, so you can't do ground moves out of it.
Sorry to Mitsurugi, and anyone else. Wasn't trying to fool anyone. I must of fooled myself, 'cause I remember I made the original post right after having double-checked, in-game, that it was possible to do. Whatever, it was half a year ago. I'll just chalk it up to delirium from those sleepless cram nights I was doing.
TKing a DB or a KJ is better anyways, for hitting people trying to poke you out of your dash.