Im not sure if an RN can challenge the NREMTP test or vice versa in AR (I'll have to ask an RN to be sure)
But if you really think about it, an RN and EMTP have same knowledge, with the EMTP being more proficiently trained in handling the cases fresh, and to handle more traumas.
When you take the EMTP education course your pretty much taking the same book courses an RN student takes during their last two years. Given that as an EMTP your going to do procedures and RN wouldnt/couldnt do, and an RN is going to do procedures an EMTP couldnt/wouldnt do.
I think it just really boils down to working pre-hospital or hospital. Both RN and EMTPs have their pros and cons. But if your leaning to nursing then get the RN, if your leaning towards the lights and sirens, get the NREMTP. If your hearts truly not in it, then you wont enjoy it as with anything else in life.
-CP