I use the underscore and hypen system on all of my CMS sites (and most static sites actually), there seems to be no harm in using either or both at the same time.
I think the main thing is to structure the urls the same across the entire site, if nothing else it make sense to the user (and to you when you try and find a bug)
example 1
Example2
on a side note the latest G toolbar PR release has given 80 of the content pages a PR of 3, so it works (so far so good)