Patrick, I have a dual degree: Biology and Nursing. I'll say the bio degree has not done anything for me lately, but you can major in both during school.
The NCLEX has very little to do with science, and a lot to do with nursing and priorities made based on science (mostly human physiology). With the information learned in my biology degree, I would not have passed the NCLEX exam, maybe the MCAT, but not NCLEX. The basic biology in a BS biology will not teach you the thinking you need to know to decide which patient in a disaster is beyond saving, which one has immediate priority and which one can wait (typical nclex fare).
I really enjoyed the biology classes. It was a way to "get away" from some of the rumors and competitiveness that goes on in the nursing programs
, and to expand my brain. So, why not major in both? You can do it, especially if you are organized and plan ahead.
Also, you may enter college and take a class and find that it fascinates you more than you anticipated and it could entirely change your career path. I've seen it happen to several people!\