Neither is required to get into USAFA.  I believe Private is on the activities list for the application.  That means it will be one more positive thing on your resume.  Most people here do not have their PPL, so it is not extremely important.  It is a good thing though.

Grades are much more important to the admissions department.

raimius is correct, you don't need a PPL at the academy.

They do have a powered flight program as well as a soaring and parachuting program.  Let me know if you want more info, I work at USAFA.