I think it definately will be a based aircraft with local crew. I dont have any specific information, but i think that anything Belfast will be kept totally separate from Dublin, due to issues in the past with unions and all this type of stuff.
It depends which way it operates. If it operates from Belfast direct to the states then yes it would probably be a Belfast crew. However if it operated via Shannon for example or if it originated in the south and operated via Belfast it would have to have a southern crew since Belfast crews aren't allowed operate any flights to airports in the republic as part of the deal with cabin crew (because belfast crew are paid less and are on inferior terms).