I am not so sure about this. It’s been sometime since I read in depth on the subject of Irish history – I have been focusing on alot of theological work lately – but I seem to recall the very reason for the bond of the Old English and Gaelic Irish originated out of the events of Protestant Government.
It arose out of the Old English Catholics’ disillusionment with the King’s policy towards them (Basically he didn’t trust them - that old ‘double allegiance’ conundrum - but he was quite prepared to bleed them dry financially to finance his wars, and they paid up to prove their loyalty.
Not to mention, the strongest loyalist – small ‘l’ here – force in Ireland was, guess, Gaelic, Irish, Catholic. Most of the young men who put down the Republican rebellion in the late 1700s was made up of young Gaelic Irish.****I presume you mean the 1798 rebellion? Don’t know what you mean by ‘Gaelic’ in this context. The rebellion was chiefly in the north-east of the country where it was largely Presbyterian and non-conformist in character. It was put down by a mixture of local protestant (established church) militias and British army andmilitia forces. There were also other uprisings in the east (Dublin, Kildare, Wicklow) and south east (Wexford) of Ireland, largely Catholic in character but with a mixture of Catholic and Protestant leadership. Again, it was put down by local protestant militias, British mercenary forces (the Hessians) and other regular army forces and militias. Perhaps you are thinking of the North Cork militia which was sent to put down the rebellion in Wexford? The rank and file were recruited from the Kanturk area of north Cork and many spoke Irish but their commanders were protestant, often of the Orange variety. They suffered a humiliating defeat at the Battle of Oulart Hill in Wexford, at the hands of poorly armed rebels whose successful strategy was largely devised by a Catholic priest. While the North Corks might be considered ‘Gaelic’, they could hardly be described as having ‘put down’ the rebellion ****
I will use the
Confederation of Kilkenny as an example - it rose out of a ‘rebellion’ of the Gaelic Irish of Ulster in a bid to reclaim their land that was confiscated by the Protestant Parliament in England. A rebellion that led to a union of Old English and Gaelic Irish determined to preserve their religion and defend their rights and property under the monarchy and within the constitution.
The alliance between the Old English and the Old Irish during the Confederation of Kilkenny was an uneasy one - the two groups had little in common politically or even in the practice of their common religion. The Old English, especially those in urban areas, were foremost in the practice of counter- reformation Catholicism, while the Old Irish were little influnced by Trent.
Granted, it was rather confused, and it was to an extent uneasy, not to mention it did end up becoming a third force in Charles I’s own war on the English Parliament. But you get the picture.
Something that Republican propaganda has wreaked havoc on in Irish history, is that many, many of the Gaelic Irish were desperately loyal to the Crown - indeed, it is exactly that reason that honestly accounts to much of the ferocity of the later Cromwellian supression. Sir Phelim O’Neil, the first Ulster Gaelic Irishman to take to the field, had insisted on his opening call to arms that the rebellion was in no way directed towards the king. And even before the Old English had properly joined the rebelion the leaders of the Gaelic Irish had introduced an oath of association which read: “I further swear that I will bear faith and allegiance to our sovereign lord King Charles, his heirs and successors, and that I will defend him and them as far as I may, with my life, power and estate.”… The confederation fought under the slogan
‘Pro Deo, Pro Rege, Pro Hibernia’. And by ‘king’ they meant the man who was both simultaniously king of both Ireland and England.
A seperatist nationalism was no part of their outlook: they were fighting for only what they regarded as their rights under the British Crown. Patriotic love of Ireland was to remain, wholly compatible with loyalty to a British monarch. A prime example would be Daniel O’Connell in the 1800s.
To be fair to O’Connell, while he was appalled by the violence and bloodshed of open rebellion, he nevertheless advocated self rule for Ireland through his Repeal movement (repeal of the Act of Union 1801)
Anyway. My overall point, appears to be

, that loyalty to the Crown was not exclusive to the Gaelic Irish.
Again, I’m confused by your use of ‘Gaelic’ here. Do you mean that loyalty to the Crown was not exclusive to the Old English Catholics and Protestants and the New English Protestants but was sometimes shared by the ‘Old Irish’?