First let me apologize if I get anything wrong, but this is how I understand Threads.
Short answer is yes, they can.
Longer answer is, they can if:
1) They use the option to "become a user". This is generally used to help troubleshoot a user's login problems or display issues.
2) They access the database directly, which contains all the data, including PMs.
I may be missing some things, but that's what I can think of.
It's like any administration position, server, email etc. If the admin has access they can see everything.
In my opinion a good Admin wouldn't intrude on the privacy of their members. It would only harbor mistrust and drive members from the boards, which isn't the idea of a forum anyway.
As far as the version of that particular board you linked, I have no idea how to tell, since they've removed the copyright and version information, which if I understand correctly, is against Infopop's rules. But I'm no expert on that. Someone else here may be able to tell where I can't.
