St Patrick is equally revered by both Protestants and Catholics. Just because he is called a "Saint" it doesn't necessarily mean he is an exclusively Catholic figure - many of the old Saints, like George, Bede, Cuthbert and David never went through any formal beatification process in the same way modern Saints do.

The largest church in Ireland is St Patrick's Cathedral, a Church of Ireland (e.g. Protestant) cathedral in Dublin. The fact that this cathedral has not been renamed is, I think, enough evidence to show that Irish Protestants have no problem with St Patrick.