Civ2 came out before the 9/11 attacks and before anyone had even heard of Al-Qaeda. I bet they'd be reluctant to have such a unit now. Would it be fine having a Middle-Eastern civ with special unit 'Al-Qaeda terrorist'?
When you say IRA guerilla, you most likely are refering to the original IRA (1919-22) and the (justified) fight for Ireland's independence. However, most people (in the UK anyway), would associate it with the more recent incarnations and the 'Troubles' in Northern Ireland (which led to 3,526 deaths, of which 1,855 were civilians (
source)).
The fact that the USA failed to take action with regards to IRA funding (until after Sept 2001) is lamentable. However, it doesn't justify terrorist attrocities.
Is the IRA really the only thing that springs to mind when you thing of a Celtic civ?