That paranoid? ☺ Well, can't say I blame you.

The only evidence for most of the actions taken, though, is the moderation log, and there's no way of telling whether the admins have a private fork of the site's code that allows them to modify that log, so that's an immensely difficult task.

I suppose you could download every single post and comment made, and then check when they appear and when they disappear and build a log that way, but how can you tell the difference between user removal and mod removal? And then you'll have to take into account the spam filter catching stuff… it's really quite non-trivial, unless you sneak a backdoor into the Saidit code for the purpose of checking this data, and manage to get it past the admins by justifying it as doing something else; I doubt you could easily get something past /u/d3rr. But even if it appeared that you had, they might have secretly modified that backdoor to report what they wanted you to see…

So really, the best bet is to implement decentralisation, and host your own Saidit. It's the only way to be sure.