What does "reveal" do from, e.g., the services menu? "Reveal" seems to be an alternate action to "open" - except it just opens some random thing that I have no control over. For example, "revealing" a ruby file in the Finder opens Path Finder (the third party Finder replacement).

So, what's it supposed to do? Can I have any control over how it functions?

I'm on Mountain Lion, but I think this is a long-standing action.
This is a Pathfinder feature that's designed to bring up the contents of your current Finder window in Pathfinder.  There's no documentation for Pathfinder, so you'd have to check with their support team to see if it could do something different.