Not as far as I know - Morgan is MOR-gan, and I've always heard Morrigan as MO-rih-gan.(Anyone who lives closer to Ireland than I do - which isn't hard - can feel free to correct me if I'm wrong! :-D)
Despite the plane ride to Ireland, I'm betting it's Mo-rih-gan. Somehow I remeber that as the pronunciation from a movie. Could still be wrong but I doubt it.