As for HTML designers that use Dreamweaver - for my experience they feel quite comfortable about HTML::Mason. I have explained them that mason-components are like their own Dreamweaver library items, but much more powerfull and they ate this :) Your example of "bad component" could be titled "bad library item" or so because it has nothing mason or even perl specific, it is an example of ugly decomposition of a page.
Be sure, it is possible for designer to learn something about Mason or ColdFusion or ASP or JSP or what-else-those-programmers-use. Don't hide too much from them or they'll lose logic of your application. Yes, they are not just page designers, the are a part of a team that creates something bigger than these pages.