Many of us asthmatics have used an expired inhaler from time to time (check out this post). I myself -- before I became a gallant asthmatic --have found an old inhaler stuffed in the couch or under the bed from time to time. And used up these inhalers under the guise of "no point in wasting good medicine."
However, I would not advise using an expired inhaler. Usualy the pharmacy will note the inhaler to become expired a year from purchase. The reason is at about this point the chemical components tend to change, and this makes the medicine less effective. Technically, at this point, there's no guarantee what you are putting into your body.
If you've used an expired inhaler, you may have noticed it tastes funny too. I like to describe this taste like rotten mints. If you use an inhaler and it tastes funny, chances are it's expired and you should jettison it. Newer inhalers should also have expiration dates on them.
So, to answer your question: No! It is not ok to use an expired inhaler!
Any further questions please let us know.