<p>Is it possible to enumerate all the current errors being displayed through an "Error Provider" without having to access the controls?</p>

There is a summary validator that will give you all of the errors, but it's pretty ugly, and I'm not sure if you can use it without displaying it on the page.  Technically, if you are doing things the "right way", all of you error handling should be handled in your midddle teir and then bubbled to the screen that way, so you already have access to all the errors in a collection or dictionary.