Just a couple of items which might interest you.
In the 1901 Census, Thomas Keegan's occupation looks like "Stoker, Electric Tram Station". I would reckon that he was employed by the DUTC (Dublin United Tramways Company). They had operated horse drawn trams in Dublin but started converting them to electric trams c. 1900. They had a Tram Depot on Shelbourne Road, Ballsbridge, which is just across the river (Dodder) from Keegan's Lane.
I also notice that you got a reference from Colette to a possible death date for your grandfather, Thomas Keegan, in 1937.
There is a headstone in Deansgrange Cemetery which may refer to that death. The information on it refers to:
Maureen Keegan, died 13th March 1928, her parents Thomas Keegan, died 22nd October 1937 and Mary Anne Keegan, died 6th January 1948, also Baby Terence Shortt.
Info from Memorial Inscriptions of Deansgrange Cemetery, Vol 5, publ. by Genealogical Society of Ireland, March 2002.
Hope this is of help