http://www.as-web.jp/supergt/155474
According to Autosport Web,
the reason of #30 Toyota Prius ran without hybrid system was because of the risk of system error caused by heat problem during the race which potentially affect the system. Also, as the local team at Suzuka (through Toyota Corolla Mie sponsorship), surely the team want to finish the race in front of all attended fans.
Would be glad to be corrected in case of wrong translation.