Well the plants and bushes in both OFP and Arma do not have classnames because they are not configured with one in any config.bin files.
There are various objects in both games that do not have classnames for the same reason, but they are normally used instead as .wrp embedded objects in the island .wrp files and for this reason do not require to have a classname declared in a config.bin file.
The model files for these objects declare what class type they are within the .p3d model file, so the engine knows what to do with them when it encounters them in an island .wrp file.
Consequently using commands such as typeOf and isKindOf, which both require a classname to work, will not give you anything useful as a result.
Incidentally, there is a second format for the isKindOf command which I added to the comref yesterday, though it won't help any to resolve this issue.
Hope this has shed some light on the reasons why you fail to get a classname returned.
Planck