I have heard native Irish speakers pronounce Uilleann several ways, but never anything close to weelyun. Either illan or uleeyan would be fairly close. The word actually comes from the word "uillin" which means angle or elbow. The appropriate name for this instrument as Gaeilge is "pib uilleann". In the early days of their developement they were often referred to as the elbow organ. This is due to the fact that one of the uses of these pipes was to replace the organ at Mass. Many of the parishes either couldn't afford an organ or were not allowed them by those that were attempting to rid Ireland of Catholicism. They were also used at the hidden Masses that the Irish Catholic was forced to endure.