I think your husband should focus on just getting to know his daughter first, so that she can understand that he's Dad.
Your husband's goal should be to become active in his daughter's life, whatever happens with Mom. He should exercise every minute of visitation he can, and jump through whatever hoops CPS throws his way. Until he's at the point where a therapist clears him for overnights with the child, I think filing for custody is jumping the gun.
And if miracle of miracles, Mom cleans up and gets her act together to CPS's satisfaction before that happens, and regains custody, Dad should file for visitation.