Official response from Ian on SCDA equipment:

Belts - whatever the drivers side has the passenger side MUST have.

Seats - whatever the drivers side has it is highly suggested that the passenger side has. This is what most instructors require. It IS however, up to the individual instructor WRT to the seat. If no instructors will ride due to non-matching seat specs, then 'lead - follow' instruction will be required.

In summation for a race car with 5 point belts - stock belts NOT acceptable on passenger side. Stock seat ACCEPTABLE on individual instuctor basis but not recommended.