This did happen to me once. Nice big juicy vein, easy stick. But when I tried to run my meds the pump kept beeping occlusion. I unhooked it, flushed, but if I released the flush it pushed back. Bright red blood. It was an artery. Pulled it out and started over. Lesson learned. Palpate to feel a pulse if you're not sure because sometimes those arteries look like big beautiful veins, but they're not.
As as far as running meds through doing damage, I'm not sure. I suppose it would depend on what's running, how much, etc.
But bottom line is, your medication is ordered IV and that's how it should be given.