I think by running just the oar rights, with no sleeves, you might run into some pretty fast wear of a fiberglass shaft from the locks. I'd want something there.
Under NO circumstances would I use tacks on a fiberglass oar shaft, or for that matter a wood oar, either. In fiberglass, I think you'd do more smashing than holding by nailing the leather to it. In wood, the tack is creating an entry point for moisture, and that tiny bit of moisture, over time, is enough to critically weaken your oar. One day, when you really want a stroke, your oar will snap right at the lock. If you want to leather your oars, see this post: Oar Leathering 101