Yes, everybody has access to Hide and Unhide. It doesn't quite work the way that we want it to yet -- the current version of Hide collapses the conversation to a single line, but doesn't actually remove it from the page. That collapsed line is still a pretty shiny button that says "Click here to see the bad thing". :)
So we're going to make a change very soon that will actually take the Hidden topics off the page, and just have them accessible in the board history and contributions. I think that's a better match with the way it works on talk pages.
Danny