If your flight is one which clears immigration and customs in Ireland then you will arrive as a domestic passenger, yes. If not then you will arrive in the US as a normal international passenger and will have to clear immigration and customs at JFK.
The Aer Lingus website, for example, states that only flights departing Ireland before 16:00 are eligible for pre-clearance. Not sure if that is only relating to EI flights or all flights, though.