The raspberry is powerful enough to handle the bitcoin verification itself, however may lack network connectivity.

The triggering of a output based on a bitcoin payment is easy enough, use any of the notify services to call your url and verify the data.
Can be made to not require a incoming connection if its behind a firewall etc.

But ofcause that requires the monitor service to be running, and then you might as well do it without the bitcoin part.
Not sure if any of the light systems are opensource and used widely enough to be an option ? (closed source propriety servers are not)