getting to the point of which FLASHES work with ETTL II I think you'll find that any E-TTL I compatible flash will work with E-TTL II camera body in E-TTL II mode as the "II" part is an process inside the camera that uses a preflash pulse from the strobe.
So so long as the flash can generate the required E-TTL (I or II) pre-flash pulse it should work correctly.
Canon will not guaranty 3rd party flashes will work (same as 3rd party lenses) but I've not heard anything bad about it from retailers.
Note that if you use a flash that the camera can't recognise as E-TTL (I and/or II) compliant the camera drops back in to TTL or manual flash metering mode.
I have three old, pre E-TTL II Canon EX flashes (550EX and 2x420EX) both models only mention E-TTL in their manuals (I think it was just E-TTL not E-TTL I as before E-TTL II came out it wouldn't have been called "E-TTL I")
Using them on an E-TTL I bodies (D60 digital and EOS 5 and EOS 10 film) they exhibited the documented shortcomings of E-TTL I (blown out reflective surfaces, underlit subjects when strong ambient back light)
Using these same flashes on E-TTL II bodies (20D digital and EOS 33 (elan) film) they showed a general and significant improvement in accurately exposing the subject.
so my belief is that the differences between E-TTL I and II is purely "in camera" and that , so long as the flash works under E-TTL I it should work correctly under E-TTL II.
of course, this could be, possibly, that the later models just were able to meter better in the first place even when reverting back to E-TTL I mode???
Bob Aitiknis site does list all the older (Canon branded) E-TTL I compatible flashes as also being E-TTL II compatible so I'm guessing the same will apply to 3rd party E-TTL I strobes
http://www.bobatkins.com/photography/eosfaq/ex_speedlites.html