You are right, his real name was Marin Duval (changed to Mareen Duvall in America). In my research (which included consultations with a genealogist in France), there has yet to be any definitive proof of Marin's parentage.
I did find a reference to Supreme Court Justice Gabriel Duvall (he used DuVal as his spelling later in life) who discussed using the coat of arms (this is gong several years back in research, so I could be fuzzy on my memory of this). He was a great grandson of Mareen and may have been told about its validity from his father or grandfather.
I don't think there is anything official. However, the genealogist in France told me this:
"The [important] information, for me, is that [Marin] was schooled in letters. In France, at this period, around 10-15% of men can sign. It is a indication of bourgeois or nobility origins."
So he was fairly certain that he had a noble background...so a coat of arms could be consistent with that perhaps.
Sadly, as Marin was a Huguenot, birth records were spotty or nonexistent at that time. There are some protestant temples with birth records in regions near to where he was rumored to have been from; but I didn't have time to look them up and do further research. My genealogist was not confident it would be worth the trouble for the off chance I would get lucky. I may pick it up again someday, though.