It is a bad sentence. It is ungrammatical and unnatural with 을 in it. If you drop 을 and make it 피자헛 샐러드바 as you said, it is a perfectly good sentence. Alternatively, you could also say 한국에 와서 피자헛은 샐러드바에 횟수 제한이 없다는 것을 알게 되었다 for the same meaning.

(moved to answer)