These two are definitely optional as the UAG will send client sessions on to the configured Connection servers without enabling these items.
BSG UDP Tunnel Server: This will be used when a connection(s) hit the UAG on a low bandwidth connection to provide a better experience for the end user/client.
Enable Tunnel: If the Horizon secure tunnel is used, change NO to YES. The Client uses the external URL for tunnel connections through the Horizon Secure Gateway. The tunnel is used for RDP, USB, and multimedia redirection (MMR) traffic.
Hope that helps.