This is certainly an interesting topic.
A landmark case that I would think would be at least tangentially relevant to an argument IN FAVOR of letting a convicted felon sit for the bar would be Johnson v. Avery; 393 U.S. 483.
This was the case that struck down a prohibition against so-called "jailhouse lawyers," i.e. prisoners helping other prisoners prepare petitions.
The theory is that it would be unconscionable from an Equal Protection standpoint to disallow an illiterate felon from getting assistance from a literate felon.
In other words, to me, the case is saying that "The smartest guy on Cellblock D"--who is not necessarily a lawyer or ex-lawyer--is better than no counsel at all.
If one were citing this case, a case would have to be made that the ex-felon planned on doing a lot of pro bono
and community service work--perhaps planned on becoming a public defender.
A side-note in this case, I believe, was that the judge felt that prisoners doing research and writing petitions was much more constructive than some of the alternative things they COULD be doing.
You could make the tangential argument that lawyering has a rehabilitative quality on the ex-felon, by conjecture. (And not many batteries occur where the weapon of choice is a Black's Law Dictionary.)
In my opinion, since we let convicts become undercover cops--where they can have legal authority to restrain a citizen--we should surely CONSIDER whether they can become lawyers.
(In jurisdictions which allow it; I would think it would be a factor whether the violation was a MALUM PROHIBITUM or a MALUM IN SE. For instance, marijuana was not even illegal in the US until 1931. Lincoln could have smoked marijuana in his law office, and not gotten disbarred. Should felony possession of marijuana be a total block to bar membership? Clearly, that's a MALUM PROHIBITUM.
"Aggravated assault," on the other hand, has been a MALUM IN SE since the inception of common law.)
FOOTNOTE: A famous attorney who was disbarred and then re-instated is obviously Frank Ragano:http://www.spartacus.schoolnet.co.uk/JFKraganoF.htm
(Note: I do not necessarily subscribe to the JFK conspiracy theories on the above page.)
Ragano, of course, is evidence of my "MALUM PROHIBITUM"-theory; to wit, alleged income tax evasion is a "malum prohibitum," since the US did not have income tax--and somehow survived--until the early 20th Century. (That's a century and a half of "Republic" without the "malum prohibitum.")