A flowing hydrocarbon like diesel or gas generates a static charge. It would be proper to ground the deck plate to the tank. The marina fuel hose should also be grounded for this reason.
Airports and home heating
trucks often have a separate grounding wire with a clip which is attached to the plane, so the ground is obvious and intentional.
Whether the tank should be grounded to the boat's house ground is subject to debate. It would literally be a floating ground if you are not on shore power
Due to the low vapor pressure of Diesel, it is safer than gas when the tanks
are being filled. The drain wire gives the electrons somewhere to go, instead of building up a high voltage charge, which eventually generates a potentially lethal spark.