OK, had a look at my notes. From the will of Mark or Marcus Cassidy, Formerly of Derry but in 1789 was living in Newtown Avenue Blackrock, who was married to Mary Anne Hussey, sister of Dudley Hussey, Recorder of the city of Dublin, we find that Hussey had another sister, a Mrs. Hughes, who was married to a Paul Hughes Esq. They had a son, Dudley Hussey Hughes of Blackrock who was buried on 11 may 1818. The will abstract in the Registry of Deeds (Ireland), P. Beryl Eustace, Eilish Ellis - 1954 is very interesting. Cassidy left money to a lot of people, including his postillion. Unfortunately I did not take a copy, just notes. But some one on this board may have a copy, to see if there is more info about Dudley Hussey Hughes. Anyway, this is an instance of the whole name being passed on.
Dublin street directories may be of help here. Irish Marriages H [ Marriages ] : Free Genealogy Pages from an Ulster site gives:
Hughes, Dudley Hussey, Black-rock=Watson, Helena, Bride St. Nov. 1807 p. 703. So if you have any of these people in your tree, that might be the explanation.
There is also an American family see- "Genealogy of Harold Dudley Hussey." H.D. Hussey. - check it out in Google for refs- but as their Dudley + Hussey arises out of a marriage much later than the people I mention here, I think that is just coincidence, but could be your DH rather than John Darragh's son in law. Hope that clarifies things. I have a family tree (not my own family) for some Irish Husseys starting with Nicholas Hussey of Mulhussey around 1400. Think maybe you should make this a separate thread.
PM