Is there a hand tool for xcode's storyboard (scrolling without scrollbars, PDF style)?
It depends on what type of mouse you're using, but on my magic mouse, I can scroll the storyboard in any direction by dragging one finger over the mouse.

You can also move it around with the command key and arrow keys:

⌘ →   Scroll right

⌘ ←   Scroll left

⌘ ↓   Scroll down

⌘ ↑   Scroll up

Note that you'd have to give the storyboard focus first, by clicking in a blank area.