Mathieu,
It is not clear to me what you are trying to achieve. Are you authenticating wireless clients or administrators or trying to do something else? What authentication methods do you want to use?
Can you post some configuration? Can you post the error messages that you see?
I'm pretty sure that Instant should work with ISE and NPS, but still it is important to know what feature you want to implement in order to help.
You may contact your Aruba partner or Aruba TAC to find out what is preventing you from doing what you want to do.