This it is indeed. Well they could. There is nothing in the grammar which forbids this. But it is preferable not to use the language like this, if only because it puts a greater burden on the audience to interpret what one is trying to say, which of course leads to possible misinterpretations. They are signals as to how the speaker feels about the person being addressed or discussed, and so are really indicators of emotion for that person.
Many European languages exhibit a certain dichotomy in their pronoun forms.
Degaspregos gets around this by a rather nifty way of using the Genitive case, which would act in combination with the other cases, and thus can actually act like a specialized adjective ending without actually being one.