Was F5 function key assigned to widgets view in old OS X?
Was always F4, as far as I can recall.

My 08 keyboard has it printed on the key itself - same layout as this picture



Prior to the introduction of the aluminium keyboard in 2007, there were no icons printed on the keys, so it would be hard to say for certain - but as Snow Leopard was 2009, it would be unlikely it would be anywhere other than where the printed key indicates on anything later than Leopard, 10.5, which would have been roughly coincidental to the introduction of that keyboard design.

The Evolution Of Apple Design Between 1977-2008 would appear to support that.