Political marriages are really more about numbers than policies
Before that, Bertie Ahern and Enda Kenny were setting out their stalls in relation to not going into coalition with Sinn Féin. This whole thing is like a political mating dance, but history tells us that when the election results are in, the parties will usually hop into bed with any party, or parties, that have the numbers to form a government.
In 1932 — six years after Eamon de Valera resigned as president of Sinn Féin to found Fianna Fáil, and less than 10 years since the civil war — the Labour party propped up a minority Fianna Fáil government. They had no trouble with Fianna Fáil then.