Basically, there are two NFPA Standards, outside the NEC, that apply: NFPA 30 and 30A. NFPA 30 applies to the storage and 30A applies to dispensing. They are referenced in the FPNs to the titles of Articles 514 and 515.
Because diesel generally doesn’t require classification, it probably can be ignored from an electrical area classification perspective. It still will have some basic storage and retention requirements though. The gasoline storage may need electrical area classification attention – the gasoline dispensing definitely does. Without knowing the details of the installation it’s difficult to make a more definitive answer.
Robert B. Alexander, P.E.
"I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)