Anyone every use a spotting scope for an autoguider? Not sure why it wouldn't be more in use, I mean, 80 mm APO, light, F6, 1.25" eyepeice. Why wouldn't someone use for instance one of the celestron spotting scopes?
Honestly, all you need out of a guide scope is that you can stick the camera into it and get it to focus on astronomic targets. Everything else about image orientation and the likes is handled by the software when you "calibrate" the guider. This is especially true about PHD or MaximDL, these will calibrate to any guidescope with any "optical plumbing" in the way.
So when you choose your spotting scope, pick one you can take the eyepiece out of. The rest doesn't matter.
PS: spotting scopes typically have a 45deg erecting prism in them so that terrestrial targets aren't upside down. I got a 102mm spotter that I use to guide now and it came with a removable 45degree prism. The only slight problem there is that the prism may have a seam in the middle of it like mine has in which case you don't want to guide on a star close to center of the view.