Just took a set of Zipps out of the box. It surprised me that it didn't have the cassette spacer for 10 speed cassettes, so I installed the one from the wheels I removed (Kysriums). It seemed to really push the last cog past the end of the freehub body. I removed the spacer to see where the cassette was oriented with respect to the freehub body, then put it back on the Kysrium with the spacer, and the two wheels seemed pretty close. I re-installed the cassette without the spacer on the Zipps, tightened the lockring, made sure there was no play (there wasn't, again with a 10 speed cassette and no spacer), and with a minor tweak of the rear derailleur, it shifts fine.
Long story short, does it seem odd that I don't need the spacer? BTW, I have checked Zipp's site, and it does not give any information about the 208 hub being (or not being) Shimano 9 speed compatible.
Any insight is appreciated.