You can, but you should know a rebar is just a recycle metal an since use for construction it not much matter its composition.
So, it is possible to have very poor quality steel or maybe if lucky you can get some higher carbon content which would make it heat treatable.
I think if you just want to use for practice and making a arrowhead that will not need sharp edge or very hard point (for armour piercing) you can make a point from it, no problem. I think most commercial target points you buy are made from low carbon steel anyways, they always blunt after hitting something hard.
Btw, easy way to test your steel's carbon content is by grinding it and watching the sparks. If it not spark very brightly it has little carbon, more wild and bright spark means it has more carbon and possible to heat treat.
