Just FYI: Search is working for all the other existing site collection except for this new site collection with it's own search scope. As a farm admin I can do search and get result back.
Basically no result for any other users. (this article wont help since search service app is working. http://www.kanwalkhipple.com/blog/Lists/Posts/Post.aspx?ID=28)
Added a visitor account in the visitor group (which is read only). This guy can go through all the libraries and see all the contents (which is good). Actually, I added few other users to different group and it seems everything can read data when they click on the doc lib or list but search returns no data to them.
Now in the search all he gets "We did not find any results for keyword".
I can login with sp admin or my account (site collection admin) then I see all the desired results.
Permission? but visitor group is allow browse through all the document libraries and they can see the metadata and open the pdf documents.
Site collection is using a dedicated scope.