Can adjectives be used as objects in English?

No. Adjectives cannot be objects; the objects must be nouns or pronouns.

In I am hungry, hungry is the predicate, not the object. Remember, linking verbs (be, am, is, are) and some content verbs used as linking verbs (such as look, taste, smell, etc.) are followed by predicates, and predicates can be nouns and pronouns , can also be an adjective.