As long as you have return tickets within the three month visa limit (can be extended to six months), then it should be no problem on entry to Jamaica. Homeland Security, on the other hand, might be curious about your travel plans.
I have entered Jamaica without a return ticket and it is just a minor hassle. We were having contract work done and I didn't know how long I'd be staying. The immigration official questioned us a bit and then let us in. We filled in the return stub info before getting to the airport for our departure. It was all good.