I don't think so, AIUI. The page is decrypted by squid to serve it, so security is irrelevant.

Also it can match on regular expressions <http://www.squidguard.org/Doc/expressionlist.html>

If I'm wrong about the first point, please clarify. Web/HTTP is really not my area so maybe squid receives and passes stuff through entirely as a blob, if https is used.

Edit. What dgoldstein0 wrote suggests I do misunderstand.