Let $\mathcal{C}$ be an additive category. Is there a common name for objects $P \in \mathcal{C}$ with the property that $\hom(P,-) : \mathcal{C} \to \mathsf{Ab}$ is right exact, i.e. preserves all finite colimits?
If $\mathcal{C}$ is abelian, this reduces to the requirement that $\hom(P,-)$ preserves epimorphisms. That is, we have the usual notion of a projective object. But in general, right exactness of $\hom(P,-)$ seems to be a stronger condition.
Kelly [Basic concepts of enriched category theory, §5.5] makes the following definition:
On the nLab, such a thing is called a tiny object. Perhaps a variation of one of these would be appropriate for your notion.