It will depend on how old those tickets are. If they have a magnetic strip on the back which is similar to what you'd find on the reverse side of a credit card, you should be able to use them at the turnstile. If they are older tickets like the World Passport tickets of the 80's and 90's where your pass actually got stamped at the gate, you would need to exchange them at Guest Services prior to using them in the park. Passes that do not have the magnetic strip would not work in the FastPass machines.
If you have a waterpark plus still left on an old PHP pass, it never expires. If there's any question as to how many days are left on your pass or whether they are still good, go to Guest Services and have them check it for you.