I've seen platties housed with angels with no problems. Swordtails are similar to platies, so there should be no diffrecence. However, angels will become agressive from time to time and your swordtail might end up being bullied by them. I'm observing this in my angels-gourami tank.
Platties/swordtails will do best in a 1m-2f ratio. More males will act agressively among them. If they breed, the angel will eat the fry in no time