That website is still listed as a web wallet on BTG's website. I moved most of my funds out of there but left some BTC in to see if anything happens. Hopefully not but no one can confirm or deny if that site is legit ?
Yes it is listed on their official site here:
https://bitcoingold.org/downloads/ under the
web tab, So its legit. [
Bookmark it to avoid phishing links]
Don't worry!, as the below statement says, They never receive your private keys and you can even run it offline. But yes its a common practice that when you expose your private keys, its corresponding address/es should be empty.
This page uses javascript to generate your addresses and sign your transactions within your browser, this means we never receive your private keys, this can be independently verified by reviewing the source code on github. You can even download this page and host it yourself or run it offline!
