Yes, though it is not recommended as a primary method. Much like other resources, Resin can drop from enemies in minimal quantities, and whilst it's nice to gain a few extra pieces here and there, it's not fast or reliable enough to be your primary farming method. This is the case for many farmable resources, and it's usually never really worth relying on NPC drops to fulfill your needs, though it can nicely supplement a farming run for animal hide or bones.