If you are only considering getting your PPL because you think it will improve your chances of getting selected for SNA, don't waste your money! Now, if you want to get your license because you want to learn to fly or want to give flying a try before you select your career choice, then by all means go for it.
However, you should go ask your class officer how the selection system works and what the formula is for rating you. You will find that having a good GPA is going to have the largest impact on your selection. So, in short, if you are worried about getting a pilot slot, study your ass off and get the best grades you can. THAT will have the biggest impact on your chances of becoming a SNA.