The Eleven-Mile Reservoir tornado was most likely non-supercell. Normally, this would have been an easy call, but ironically, a rare mountain-supercell was just off to the west of this storm. I was working at the flood center in Denver that day and there was some convection up over the mountains. I got called in because a nice storm popped up on the northwest side of town and rode the foothills due south. I was surprised to see the tornado report pop up on spotter network and then have a seemingly innocuous storm be warned. I suppose it is still possible that this storm was supercellular but the radar scan there was showing no elevated rotation.
I saved a radar image of the later supercell which traveled south along the foothills. You can see it here:
http://blog.bigskyconvection.com/2008/08/colorado-mountain-supercell.html (Click on the radar image for a large version)
You can see the tornado report well to the southwest of the huge supercell. The radar image came approximately one hour past the original tornado report .
So, I guess I'm just being devil's advocate. The environment was favorable for turning storms that day. However, there is a ton of video of this tornado (including some shot directly below, looking up) ... and all of it makes it appear to be a non-supercell tornado. Youtube it ... seriously. There's a guy on a boat right next to the thing, staring straight up. Gorgeous footage. Definitely looks like a spout.
Reports from that day.
PS: The other supercell had a tornado report ... but no one ever saw it. I could see the wall cloud from my position far to the north, but it eventually got shrouded by the downdraft and I lost sight. (I wasn't chasing, I was on a rooftop downtown Denver at work). There was damage reported, but it could have been RFD tree fall.