If you are doing it for resume padding, don't. If you are doing it because you want to and are interested, then do it. It's a waste of time for the former...being an EMT is not the end-all and be-all of getting accepted. If you are interested, you'll get some valuable patient contact and the most minimum of medical knowledge (like close to none, but better than nothing).
Last summer, I applied to AMR in my hometown two months before school ended so they decided they wanted me before I finished school. Too late for that. (They were pretty desperate...they even called me and tried to get me to start while I was still on the other side of the country). I also worked for my schools student run student staffed ambulance. What you get is some small step up compared to other students when you are in school (but from what I've heard, they catch up fast). How much it helps your application is debatable.