I keep my work Exchange-based email pushed to my iPad. Is there a way to trigger an audible alert on the iPad based on receiving certain content? For example, an email with a keyword in the subject?

No, afraid not.

You might be able to cobble something together by using rule based forwarding with your Exchange account and the Boxcar app. Looking over the app description and what I remember of being able to setup using Exchange (using exchange server rules not local), it should be possible.

You would simply set up those emails to forward or copy/forward to the Boxcar email address supplied.

That's all far behind me now, so I can't give you more detailed instructions.