Using pain to teach Aikido is a crutch. If you've broken your leg go ahead. But if you haven't, it'll look daft.
Using pain as a lesson for other things, might be useful. Learning what type of pain is acceptable to your body, and what's not. Dealing with pain with centering, kokyu and etc. Understanding pain can be a good way to avoid injury.
Theoretically, that's what I believe anyway.