The JMR course is a preparation for the JNCIP-SP exam, so it is a given you can use it for that exam.
In general, I have never seen any restriction for what exam they can be used for - but obviously not for the Expert lab exam.
I beleive the voucher will be locked to your account/email, and based on the ones I have received in the passed the expiry date seems to have been at the end of the following quarter, approximately.
Assuming you claim your code in June, the expiry date for the voucher would probably end of September or December.