Yes - This JoyTech does have spacers so that a variety of cog body thicknesses can be accommodated. For a plain "flat" cog, the proper chain line seems to be with the cog in the direct center of the splined/threaded part of the hub with an equal number of spacers inboard and outboard. Some cogs, however, have a cast-in "shoulder" on the in or outboard side of the actual cog. A single threaded locking ring tightens the spacer/cog pack against the inner shoulder of the hub.

If a threaded cog had the same diameter and same 24tpi left-hand-thread configuration, it could also (theoretically) be used on the hub. Whether or not the diameter would match is the question.

I made the mistake of ordering a variety of 3-tab cogs via eBay thinking they would fit, but it seems unlikely that they will. I also ordered one threaded cog on the (mistaken) assumption that all threaded cogs were standardized (not!). I've re-ordered the two cog sizes that I want most in the proper spline configuration as a result of this thread. Thanks for the helpful feedback.

I may still e-mail Cambria and/or Sheldon Brown with the suggestion that a "single-speed cog compatibility table" be created to avoid confusion. Even the splined cogs seem to come in a variety of diameters and cog-configurations. The Shimano Nexus/Alfine, the Rolhoff, the Campagnolo, the coaster-brakes, and the Sturmey-Archers all seem to use unique cogs that aren't compatible with the Shimano spline pattern. Despite this, they all can use the ⅜ or ¼ inch chains. Further, the cogs that DO use the Shimano splined pattern seem to be marketed using a variety of names.

All's well that ends well, so I think I've actually got the proper cogs coming to me now. It really shouldn't have been this hard, though...