I think you def need to address it. Your poor dd! I'd perhaps try to take the emotion out of it. Tell him it has been a long standing, ongoing issue which the social worker and class teacher are aware of. Tell him the steps taken in the past and what had already happened in this case. Then tell him that his words have actually further victimized your dd and given strength to her bully. Then ask what he intends to do about it and that you intend to follow up with social worker and principal (on his return).
Let social work know so dd can get extra support. Poor thing. I loath people who don't get the full story and then belittle children