hi Q-G,
Everyone in the electronics world is going through this right now. Every component manufacturer is working on lead-free components. Don't forget lead-free solder, which in many cases requires a whole new soldering process, that also has to be validated.
Does your contract manufacturer buy the components for you? Or do you supply them?
If they provide them, I would pass this requirement on to them. You won't be the only one asking, believe me. They also should tell you where they are with leadless solder. There are multiple options, your engineers should decide if what the sub-contractor is doing meets your needs.
If you're supplying the components, I would take your BOM and go to each of your suppliers and ask them if the components on the board are available in a lead-free version. most of these folks have been working on ROHS and WEEE for years now and should be pretty far along.
You should qualify all these new parts at the board level, at a minimum. Don't know how deep your Engineering group is, but being a medical device manufacturer, you probably should go right down to the component level.
Do you have customer requirements driving this? If so, they may require you to validate that the components are lead free. This is where a database of tested product by manufacturer would be real helpful, as I mentioned in a post on ROHS about two years ago.
http://elsmar.com/Forums/showthread.php?t=6526&highlight=ROHS