Hi Kelly,
It is NOT entirely true that you would need a BS in nursing to become a NP. ( BS is a 4 year undergraduate degree.)There are Master's Entry and Graduate Entry nurse practitioner programs at prestigious institutions like Yale, Penn, UCSF, Johns Hopkins and elsewhere... typically, they are 3 year programs where the first year you complete an accelerated RN program and then move on to graduate NP work in the last two years.
However, like most posters have mentioned already, they are quite competitive. They do require the GRE. I don't think ND programs require any form of standardized testing.
In California, NDs have an almost equal scope of practice as nurse practitioners. Depends on what form of NP you are comparing with ND (women's health NP, certified nurse midwife, neonatal NP, family practice NP)
I would carefully assess the philosophies of both naturopathic medicine and nursing as well as their respective scope of practices when deciding which path to take.
I believe naturopathic medicine is a growing field, yet still in it's "infancy" in the eyes of the public, and has lots of potential. If you are more mainstream-minded the NP route may be better. It's well established and in a recent (a couple years back) article in TIME or Newsweek, mentioned that there is a growing trend among consumers preferring nurse practitioners for their primary health care rather than MDs.
So, it really depends on where you plan on establishing yourself and what you want to do with your career.
Good luck!