I think I know the answer but it is just a wild guess.
Inhalants are not classified as either a stimulant or depressant, because there is such a wide range of inhalants that some are classified in different groups. Therefore, some inhalants are stimulants, and others are depressants.
Is this correct?
A description of the effects of commonly abused inhalants can be found at
http://www.drug-treatmentcenter.org/inhalants.asp
The ocategories described there are household chemicals most often abused by people, not the legitimate drugs taken by inhalation for things like athsma or bronchitis.
But do I have the right idea?
I think you do. The inhalant is only the vehicle by which the drug or chemical is conveyed.
Vehicle?