The lack of a Google acknowledgement is the best evidence. Assuming solid ranks is evidence of whitelisting isn't evidence. It suggests they did as Google wanted... "just make a great website and others will reward you".
Simply taking Google's word for it implies a level of foolishness IMO. Search any of the black hat forums for case studies, and you will be sure to uncover some rather interesting results. Same spam links pointed to different sites and the results are notably different. That's enough evidence for me that Wikipedia is whitelisted. I do however feel sorry for the other sites used in the case studies as they appear to have been hurt pretty badly.
Have you actually tried it?
What part of breadcrumbs are consider over-optimization?
Yes, Mild interlinking is great, but we have removed excessive interlinking as is commonly used on Wikipedia. Of those sites where we removed the heavy interlinking, mild improvements were seen in search positions.
Using a whitelisted domain to develop a strategy, such as Wikipedia, is severely flawed. Because it is not held to the same algorithmic measurements as the majority of sites are, the results are much different for ordinary sites (over-optimization penalties).