Nope, Great Shield will block the snipe damage. While damage to the bench ignores weakness and resistance as per the rules (it also says it on the card), it is still subject to any other effects, unless stated otherwise. Aegislash-EX's Ability Great Shield does not require it to be active in order to have the effect, so the damage would be blocked. Do keep in mind however, that unlike Safeguard Pokemon, and like Pyroar FLF's Intimidating Mane, Great Shield only blocks damage. Any other effects of attacks, including placing damage counters (this is distinct from actually doing damage) will go through regardless of whether Aeiglslash-EX is active or benched.