I am not a Catholic but I will try to answer anyway.
The term dogma has a specific technical meaning: it refers to a belief that Catholics are required by the Church to accept. There are many beliefs which are not dogmas, even if they are widely held to be true.
The book Fundamentals of Catholic Dogma by Ludwig Ott (1952) is a standard reference. He lists ten beliefs under angelology.
- In the beginning of time God created spiritual essences (angels) out of nothing.
- The nature of angels is spiritual.
- The angels are by nature immortal.
- God set a supernatural final end for the angels, the immediate vision of God, and endowed them with sanctifying grace in order that they might achieve this end.
- The angels were subjected to a moral testing.
- The evil spirits (demons) were created good by God; they became evil through their own fault.
- The primary task of the good angels is the glorification and the service of God.
- The secondary task of the good angels is the protection of men and care for their salvation.
- Every one of the faithful has his own special guardian angel from baptism.
- The Devil posesses a certain dominion over mankind by reason of Adam's sin.
Among these, 1, 2, 8 and 10 are listed as "de fide", meaning true by reason of divine revelation; 4, 7 and 9 are "sententia certa", meaning theologically certain; 3 is "sententia communis", meaning commonly believed but not necessarily certain; and 5 is "certa" for the fallen angels and "communis" for the rest. No mention here of Metatron, or anything of the sort.
The Catholic Encyclopedia says under "Angels" that "no proposition touching the angelic hierarchies is binding on our faith". It refers to De Coelesti Hierarchia by Pseudo-Dionysus, and the Summa Theologica by Thomas Aquinas, as containing commonly accepted beliefs about the different types of angel; neither of these mention Metatron, or any figure fulfilling that role. All such writings are seen as speculative, and within the domain that theologians can legitimately argue about. Metatron crops up only in the encyclopedia entry for "Kabbala", but the context is explaining that it is a belief held within Judaism.
In conclusion, it seems that Metatron is very far from being Catholic dogma, or even a belief that many Catholics hold.