It's possible I am typing the command incorrectly, but if I wanted a Skeleton to spawn with a bow I'd type
/summon Skeleton {Equipment:256}
But if I add specific coordinates
/summon Skeleton 10 10 10 {Equipment:256}
/summon Skeleton ~ ~ ~ {Equipment:256}
No weapon will appear in the mobs hand when summoned.
FYI, The website is creating a space before the fancy bracket - not me