Uileann vs Union is an invalid argument as the words originate in two different languages. Uileann is gaelic, union is english. Its like the the argument over the correct name for the country Ireland vs Eire, it depends which language you are speaking. Also at the time of the development of the Irish pipes Gaelic had been largely wiped out as a language so it is not suprising that the common name would the english version.
Also it is not usual for the Gaelic name to have a different derivation from the english name eg Dublin is Baile Atha Cliath in GAelic. It also happens that the Irish word can be incorporated into the english laguage and become commonly used eg if you were looking for a town called Dicert in Roscommon you would have a problem since the signposts say Thomastown in English but the locals refer to Dicert.