The Crell program, even if he didn't have memories of the real Crell's war atrocities, seemed pretty unethical. So that's a reason to be wary of using him in future.
That said I wouldn't delete his existing knowledge. That's just pointless - it then just needs to be re-discovered in future, and lives might be lost needlessly before that happens.
re; Belanna, she has a duty to her crew. I'd be more sympathetic to her wishes if she was in a hospital back safe on earth.