It says on the hotel website (that you linked) that it takes an hour from town. You'd therefore have to leave Dublin at about 6.30am if you stay in the centre and have to be at the hotel for 8am. So if you're not a morning person, you'll need to stay in the hotel!
Dublin buses in my experience are not hugely reliable although quieter at that time of the morning and in the evening you'd be going against the traffic back into the centre but you might wish to check with Dublin Bus what time the first one departs in the morning...