How can I create a Drupal "Page" (not a block) without any theme? How can I create a Drupal "Page" (not a block) without any theme?
I do not want this "Page" to include any header / footer / left / right column.
My understanding is that this isn't possible but could I create an additional theme for my site which is just completely blank, and apply this to the appropriate pages?
We have a salesman that wants to build his own set of pages within Dreamwever and then I would apply this blank theme against just these pages without impacting the existing theme that is utilized for the other pages.
Try the ThemeKey module.

This module has a number of really useful options; relevant to your question, you can have it use a different theme or a stripped down version of your existing theme on certain paths or conditions.