Is there any difference between cargo and hull underwriting practices/procedures?

Assuming that by hull you mean a vessel that transport products overseas, yes there is a different. when underwriting a vessel, you take into account the material its made from, the route it takes, the seamen, and other environmental factors that affect its trip to the destination. 

When underwriting a cargo, assuming that you are talking about the containers that being shipped on the vessel, you take into account all the above, plus, special items regarding these containers. 

You will always account for ethics and political risk too.