The reason that poly frays is that it's woven, so when you cut it, you expose the weave (silk does the same thing...many fabrics do but to different extents). Nylon chiffon is knit, so it's easier to cut, but I'm not sure I'd go so far as to say it does not have to be hemmed...

I made a lovely cape out of chiffon (nylon) and didn't reinforce the seams. It looked really fabulous on...til I started moving and the seams started to fall apart. It's still a very delicate fabric and needs (imo) to be hemmed with a stitch of some sort.