https://admission.stanford.edu/apply/decision_process/index.html"
Restrictive Early Action Policy
Applicants do not apply to any other private college/university under their Early Action, Restrictive Early Action, Early Decision or Early Notification program.
Applicants may apply to other colleges and universities under their Regular Decision option.
Exceptions
The student may apply to any public college/university with a non-binding early application option.
The student may apply to any college/university with a non-binding rolling admission process.
The student may apply to any foreign college/university on any application schedule.
The student may apply to any college/university with an early deadline for a scholarship or special academic program, as long as:
the decision is non-binding and
in order to be considered for the scholarship or program, the student must apply in the early round or by an early deadline.
Because Vanderbilt’s ED II is binding, I believe you would be breaking the terms of Stanford’s REA.