Defining what static bypass does when going through the ProxySG vs. creating an "Allow" rule for a URL.
The static bypass list is strictly for IP addresses that are either used for source or destination. By statically bypassing the IP address on the ProxySG, (Configuration > Services > Proxy Services > Static Bypass List) you are sending the traffic through the ProxySG without applying any SG services to it. In other words, by adding entries in the static bypass list you can prevent the ProxySG appliance from intercepting requests from a specified system.
As for creating a rule to "Allow" a URL site in a Web Access Layer, the entire rule will be evaluated through the policy layers in the order in which they are listed in the Visual Policy Manager (VPM).