The mere angels are not anointed as Melchizedek-the king. Here again is a quotation from Psalm 110.
The writer of Hebrews wants to make sure we don't miss what he's talking about. The Son-Melchizedek-the Lord-the king and the angels are all "ministering spirits," leitourgika pneumata, sent forth to the service, diakonian, of those who will inherit salvation. This is a straightforward statement that he is talking about priests in temple functions who will help worshippers through an ordinance in which they will inherit the kingdom of heaven.