I guess maybe I should try the appliance forum with this question.

I may be misunderstanding the question but, what you're looking for is a chimney hood, not an under cabinet hood.

Hi live wire!

Here is a link to what I want. The range hood and the duct cover are two different pieces and are sold separately. I was wondering if I could buy a less expensive Broan pro hood (like this one - http://www.ajmadison.com/cgi-bin/ajmadison/RP130.html) and install the aforementioned duct cover above it.

Here is a link that might be useful: Range hood and Duct cover

Under cabiet hoods are attached to the cabinet above and are mainly supported by that cabinet. Chimney hoods have brackets that attach to the wall, so no, you can't use an undercabinet hood as a substitute for a chimney style hood.

Thanks green designs. Now that you have said it, it seems so obvious!