Dan, with all due respect, from the information I've seen, most of the rebar available in the US shouldn't be welded. Every project that I've worked on welding or heating the bar was not permitted. However, I suppose for residential applications it would be OK.
I don't recommend welding rebar made from scrap metal. It has to be a premium grade of rebar in order for it to be ok for me to approve welding. ASTM A706 is weldable without any additional procedure. But even though A706 is made, it's not made often.
A615 is a lower grade with high carbon content. Even though it will physically weld together with the correct welding procedure (which includes preheating), if you do it wrong it will crystalize and crack, and create a weak point along the bar. So I don't let A615 welding fly on my work because there's no way to guarantee that the guys actually bring the torch out there and preheat the metal before tacking. It's just hard to fathom that they'll follow that procedure. So, I don't allow it.
Also, a plastic zip tie costs 7 cents a tie from my local supplier, and comes in a plastic bag. A wire tie is 2 cents, and comes in a bandolier. It takes seconds to put a tie on with the $3 twister.