Hi I might be able to shed more light on this one!
I have been carrying out research on a Robert Devlin (born 1790, Drummaul) who also served in the army (including Canada) and was discharged in 1824 having served 11 years. This could potentially be the brother of the Arthur you mentioned as it would make sense for two brothers to join up, one inspired by the other. The descendants of Robert Devlin were Protestant, rather than Catholic. I have found at least three children for Robert and I have extensively researched one of these lines down to the present day.
One of his descendants has already taken a family finder test with FT DNA and another is awaiting results. Has anyone on your side tested? If so this might prove or disprove the theory!