Better ways of making a scroller
To your questions:


More options; sure you could provide a wait time to setInterval to control the speed of the scrolling down, you could also increase the scrollTop increment to make it scroll down faster.
Less code; I think this is pretty much the bare minimum, a little too bare really.


I think func and interval are very generic names, I wasnt even sure if the code works / what it does until I clicked the fiddle link.

I would counter propose the following code, it is longer, but far more readable.

var scrollDownInterval;

function scrollDown() {
  document.body.scrollTop++;
}

function startScrollingDown(){
  scrollDownInterval = setInterval( scrollDown );
}

function stopScrollingDown(){
  clearInterval( scrollDownInterval );
}

window.onmouseover = function() {
  stopScrollingDown();
};

window.onmouseout = function() {
  startScrollingDown();
};

//Start scrolling down immediately
startScrollingDown();