Can you ask for a support modification if the mother pays no bills for rent/utilites?

So my husband owes his daughters mother a ton of money in back child support due to the mother not taking him to court until the child was older. The mother lived with her parents and never paid rent/utilites so i never thought it was fair that she got awarded so much (my husband had a crappy attorney at the time). Well my husband recently filed a support modification due to a job change. She no longer lives with her parents but lives with a significant other who pays all the rent/utilies. She even admitted this in her paperwork. Can my husband ask for a reduction in Child support due to her not paying rent/utilites (otherwords, not completely supporting the child)????????