Is there a way to mouseover with an iPod touch?
It doesn't appear so. Apple's documentation says that elements must be clickable in order to have mouseover events work, and as far as I can tell, the spoiler elements are not clickable.
IMO it would be useful for this to be fixed (probably the element can be made clickable, which means that it would still work - but with a tap rather than hovering the mouse). Perhaps this needs to go to meta.stackexchange.com rather than here, though (since this is also used for the Gaming SE site and perhaps others).