As I understand it, if people visit a page, then its load speed is included in the overall site speed calculation, weighted according to have often it is visited. This is true even if robots.txt blocks Googlebot and other spiders from crawling the page.
Yes, Google is using my stats page which is the longest loading page on my site (13s) and it is only I who have access to it. The vast majority of my pages load in about 1 sec and Google reports an average of 2.3sec for the site.
I couldn't say for sure whether it is being included in the calculation or not as my home page is very long and takes about 4 or 5 seconds to load.