Brilliant stuff, Gibbo!
Yes, they were. There were two used on the Loughrea branch, though I don't know their history, I believe they were used to bring fuel in for the resident G class locos. One was believed to have a tank which originated on the West Clare, probably to bring diesel toi Kilkee to fuel the railcar which did the Kilrush branch shuttle. However, such vehicles were as far as I know, always "departmental" wagons, rather than used for commercial traffic.
As an aside, for the general readership, with no petrol industry or milk tank traffic here, tank wagons were extremely rare in Ireland, and almost all that we ever had ( a few exceptions) used for railway use.