The sender is clamped to the tank by the lock ring, if the tank is grounded the sender is grounded.
I agree that a solid ground from the sender metal to the chassis would be positive ground but the factory relied on the clips on the fuel lines to do the grounding so I would feel very confidant in the tank being grounded to supply a superior ground than the factory.
I wouldn't ground the sender through the tank. All that's making that contact are those three small tangs on the lock ring. I would ground the sender like the factory did. It'll be a better ground.
