Unless you append a "Permanently Moved" to the response, Google will not like that.  However, I am perplexed that you weren't able to get that to work, as I spent a great deal of time last night trying to break that RegEx.  It worked fine on a DNN v4.08.03 install.  I even tried adding and removing a "fake" ArticleDetails page to be able to tell you my findings in my previous post.  :(

Sorry that your result wasn't the same.

But your workaround will indeed work.  It shouldn't be necessary, but it will work.

So far, I haven't seen any evidence of Google penalizing my sites' page rank for implementing friendly urls like shown here.  In fact, my page rank increased on one site. 

What you are asking in changing a DNN url to a shorter url is indeed possible.  However, to mimic the folder path, you really need to either add a folder with a redirect, implement a module such as PageBlaster to mimic a virtual directory, or your own similar solution using wild card mapping in IIS.

However, if you can settle for a URL more like:

mysite.com/contact.aspx

That is MUCH easier:

LOOKFOR
.*/Contact.aspx$

REPLACEWITH
~/Default.aspx?tabid=123

Another thing I would suggest is making sure your tabid values are all lowercase, as the page rank algorithm has appeared to care about the casing of the "folder names" that the DNN url generates in its default rewrite.