So, in effect he granted pardons to all those people?
Not exactly. He did not absolve them of the conviction, but rather restored some of their rights.
Now, he did it carte-blanche, with no regard for case-by-case distinctions. He also did it is a very political manner, clearly intending to bolster democrat voting ranks.
I’d be pretty certain that he intends that they will vote democrat - whether they personally go to the polls or not. Such is the state of democrat politics, where cemeteries are sites for voter registration drives, after all.