At a glance it looks like it's really just a proxy, that was limited to scholar.google.com and mutates the page slightly (adds a header, sci-hub links).
I'd imagine that would be quite hard: many university libraries have their own proxies which make sure that visitors to the library are able to access the content that the library has paid for, and often modifies Google Scholar (with their cooperation, I believe) to list links to accessible versions of the content next to search results.
Does google generally block proxy servers?