There's nothing wrong with holding Rose accountable. His pre-gambling actions were more than enough to earn a place in the HoF. That he later was caught gambling doesn't change the earlier accomplishments - there's no direct link between the HoF-level play and the later gambling. To benefit from gambling he can only do one thing - lose more than he would otherwise. Gambling cannot in any way translate into more hits, which is what should put him in the HoF. If they want to punish him for his later actions, then indicate that in the HoF entry.
There's nothing wrong with holding Rose accountable. His pre-gambling actions were more than enough to earn a place in the HoF. That he later was caught gambling doesn't change the earlier accomplishments - there's no direct link between the HoF-level play and the later gambling.
We can argue the merits of the rule as much as we like. But the fact remains that the rule was in place, Rose knew the rule and the consequences for breaking it, and chose to break the rule anyway.
If we're going to discuss changing the rule, it should not be retroactive. He made his choice, let him live with the known consequences.