Hi Lisa,
Hugh would've been call Hugh Diver when growing up in Donegal or in the the Gaelic native Irish form Ó Duibhir. The pronouncation of Diver is Dee -i-ver and not the underwater version. When he left Donegal, more than likely illiterate his name was phonetically recorded by officialdom as Devers.
Diver is an native Irish clan in Donegal with pockets scattered throughout the county but more commonly in the parishes of Meevagh and Gweedore (Tullaghobegley West).