Well... returning an ill fish to a community tank is never recommended. Particularly if this fish's spine is still curved after treatment and never recovers... this could indicate that he still harbouring a virus or bacteria and spreading the virus/bacteria would be a concern with the other fish (making them ill as well).

If he does recover... I wouldn't return him to the main tank till he has been "healthy" for at least 2 weeks.

If his curved spine was always present (genetic defect)... then I think it's more of a possibility of passing on these genes to the fry. But this is more than likely caused by illness.

HTH...

Michele