I don't know a whole lot about Usenet.

Before we get to the real question, is Opera Mail a decent newsgroup client?
Anyway, if you were to access Usenet, and more specifically alt.binaries, with a hushmail account, would you be safe?

Everyone that used to order weed/mushrooms online through "Budmail", (shutdown now), had to use a hushmail account.

No one was ever caught, and hundreds of thousands of people bought from the site. So yeah, secure enough.

Hushmail doesn't make where you're connecting to anonymous, or anonymize anything. It just uses PGP to encrypt messages. If you're downloading unencrypted messages, then it won't matter.

Don't use hushmail. Setting up a decent mail client like Thunderbird or Evolution to work with GnuPG is worth it, and then you can trust the system.