A.
A good question. Where a shipper requests an airline to provide him with an airline-owned ULD for the sole purpose of easier packing, the Unitized Consignment rule applies. In the case of this question, the shipper of the human remains is not requesting the airline to give him an airline-owned pallet. The answer, therefore, is that the airline cannot charge him with ULD minimum pivot unless the shipper had requested the coffin to solely occupy a pallet load. The airline is free to load other cargo on the pallet (not on top of the coffin due acknowledged respects to the deceased).

The then chargeable weight is the dimension of the coffin or its gross weight whichever is heavier in accordance with the Class Rate rules.
Normally, airlines load other cargo alongside the coffin and share the pallet space. An airline would never put packages on top of the coffin. Even the loadable space on a pallet is thus unused, the airline cannot enforce a ULD minimum pivot charge. The airline can negotiate with the shipper but if the shipper refuses, the airline has no grounds to enforce a ULD rate on coffin shipments because of the absence of such rules supporting the airline position.