No, not exactly. Transfer those powers to each of the four Provinces - Ulster; Leinster; Munster and Connaught individually with "Ireland" only running a couple of services at the federal level, rather than to Ireland collectively as OTL and the Unionists might have agreed to a compromise. Pretty much what they signed up to in 1923 after all.
You are conflating the post 1923 Six Counties with pre 1914 Ulster. Remember that four Ulster counties had Nationalist/Catholic majorities (Donegal, Monaghan, Cavan and Tyrone), one was more or less half and half (Fermanagh, 2% Nationalist majority) and four had Unionist/Protestant majorities (Antrim, Down, Londonderry and Armagh). The Unionists of Edwardian Ulster did not want to be (a) part of a state that they feared (not without some justification it must be said) was going to be dominated by the Catholic Church; or (b) separated by protectionist tariffs of any sort from the British and Imperial markets on which their then booming economy was dependent. Reassure them on those points and perhaps a deal can be struck.
Post 1923 Ulster is a different kettle of fish. To the Ulster Protestant, the 1916 rebels are a gang of traitors who tried to stab the Empire in the back as the cream of Ulster's young men were dying heroically on the Somme. He has been radicalised by the War of Independence and the attacks on the RIC; he has had his numbers added to by an influx of Southern Unionists and former RIC men who have fled here for refuge; he has surrendered three counties in order to shore up a Unionist majority in the industrial heartlands. Between his experiences in preparing to fight not to be part of a Home Rule Ireland and the activities of people like Broy and Nelligan in Michael Collins' intelligence war he believes that it is a security risk to have Catholics in key jobs. And he is further exasperated by his Catholic neighbours refusal to accept his new state and take their seats in local government and at the Stormont Parliament. And the Orange Order has become extremely politically powerful. And there certainly is a degree of religious bigotry (I hesitate to use the term sectarian because "Ulster Protestantism" are not a sect, they are a broad coalition of over a dozen distinct religious groupings) to be added to the mix.
And, if the Curragh mutineers were prepared to resign rather than fire on the Ulstermen, plenty of other officers had expressed no such opinion. And the Royal Navy were quite prepared to bombard Belfast, Larne and Carrickfergus according to Winston Churchill.