A nicer way to integrate Tumblr feeds into a SilverStripe site would be to use the RESTFul Service class in SilverStripe to pull the feed of articles directly from tumblrs API (http://www.tumblr.com/docs/en/api#api_read).
Thanks so much, Willr. I really, REALLY appreciate it. I've got this component of the project in the development cue and can't wait to try the SilverStripe RESTfulService with Tumblr API.
FYI, for anybody who is interested, the short-term work-around (the client is rather impatient...imagine that!) I used to integrate the Tumblr blog was an iFrame embed and assigning CSS properties to the element level of iFrame in Layout.css. Not pretty, but it will get it done for now.