Rich,
Poop is correct. You may use a tent on any site. But, 3/4 of the sites (loops) are reservation only and rest are walk up only. The reserve sites are mostly vacant ONLY Mon - Thurs. Non reserve sites can be full at times. Best go to Recreation.gov and scope it out before.
Tip: Don't wait till Friday to find a non reserve site. Won't happen.
I've been here last couple of weeks and it's most always at capacity. Very crowded.