there is no such thing as a supplemental dataplate.
any attachment information is entered onto the factory dataplate by the factory.
if any attachment is added to the profile of the machine it has to be approved by the factory and a new dataplate made/purchased from them. (it is very costly, last one i had done ran around $600 and this was several years ago).
If you want it to be official it has to be done this way ONLY. Dataplates are like license tags on cars, they are very serious about that.
With that said, all the years of being in the material handling business (40+yrs) i have never seen a trash hopper/dumper classified as an 'attachment' that was required to be entered onto a dataplate.
If it mounts onto the lift as a permanent fixture and is directly tied to load handling ie: sideshifter, clamp, etc then yes that would be part of the data entered onto the dataplate. Otherwise you would have to consult with the manufacturer (or dealership of said mfg) to get the info you need.
I'm not 100% sure but i do not think any of the osha or ansi documentation is that specific about what you are asking, i'm sure they would refer you to the equipment mfg. The general description they describe is if the attachment is 'removable' then the attachment should have it's own tag with the required information and does not need to be entered on the forklift datatag as long as the attachment has one.
In this case the hopper should have it's own datatag with that required information and is not required to be entered onto the trucks datatag because it is considered a removable attachment.