I just tested that out, and it isn't working for me. I keep getting an error of "The system cannot find the file specified", though it does trigger the job. I tried using a couple of different user accounts as well, and changing a bunch of settings around.
I'm guessing the problem is that the screensaver files can't be executed directly from Task Scheduler ( When I right-click and try and Run, it doesn't work. Paste the same exact path into Explorer, it works)
A little bit of research leads me to the line of C++ code that starts the screensaver by sending a message to the desktop window.
SendMessage(GetDesktopWindow(), 0x0112, 0xF140, 0);
I'm thinking this could be translated into autohotkey, and compiled into an executable that wouldn't be running all the time.