The Nishi Seto expressway doesn't stop in Onomichi, it just dives off the mainland to Mukaishima and beyond via the bridges and doesn't bring much to Onomichi itself apart from bicycle rentals for tourists. Mihara just along the coast is a much more active ferry port with regular sailings to various islands, and that's why Mihara gets Hikari shinkansens whereas Onomichi only gets the stopping Kodama service. Mihara's shinkansen station is integrated with the local JR line station down by the docks, a short walk to the ferry port. I use the Mihara station to get to and from Hiroshima when I'm staying in Onomichi (as I will be again in a few weeks time).
The Onomichi ferries are still in operation. 100 yen to cross the Pacific, what a bargain!
The company you mentioned, was that the Hitachi-Zosen shipyard on Mukaijima next to the bridges? I've been told it used POW slave labour during WWII.