Yah but pr doesn't have crap to do with serps does it? (isn't it just an authority based rank system)Another issue is pagerank. Unless the main site has enough pr juice, a blog with a couple hundred posts in a subfolder will probably go into the supplemental index.
As long as you cross link them I think there should be no issue with seo and indexing.
Just wondering cause I have put many sites to the top of google that make money and have no page rank.