Will it be possible to extend the Argo SRV's shields around the ship that's being towed to offer extra protection when extracting disabled ships from the battlefield?

No, the shields from the ARGO SRV and all other ships in the game are currently just for the ship itself and do not cover nearby objects. Towing a ship or vehicle puts it at risk, so the environment and flightpath should be considered carefully by the SRV pilot.