We used to call the OTH an "administrative BCD." The Bad Conduct Discharge may be awarded to enlisted personnel at Special or General Court Martial. And, yes, conviction by SPCM or GCM is the equivalent of a felony.
And, one more thing, we don't know that he got an OTH. I still believe that this story may be the equivalent of LT Bush "deserting."
In which case, he never would have qualified to be elected to Congress, right? Unless his record was purged and his discharge upgraded first. I think Carter and Clinton both had a hand in upgrading not once, but twice. And his records removed by one of his sticky finger friends. Just a guess.