8 Speed Cogs on a 9 Speed Hub

[Krony]

Just bought a new bike for my son which came with a 12-21 9 Speed hub. Would like to give him larger cogs and I have an old set of 8 speed cogs from another bike. Would replace the 18C, 19C and 21C with a 19A 21A 23A. This combo seems to be OK based on Campy's manual but not sure that the cogs are intercahngable.

Will the 8 speed cogs work on the 9 speed hub?

I know I will have to use the 9 speed spacers. But are the cogs themselves interchangable?

Thanks.