Shouldn't be a problem. Clear customs and immigration. Drop off your bag in Terminal 4 in the area designated for connecting passenger baggage drop off and Emirates should take it over to Terminal 5 for you. Just be sure that your luggage is tagged with the final destination of DEN. If you have two separate tickets, you can call Emirates and give them the jetBlue details so that they have everything in one PNR. If you are booked in one PNR and have one ticket, you are all set.