Only if you want to put a ten speed cassette cluster on the rear wheel.



http://www.sheldonbrown.com/dura-ace.html

To avoid this problem, Shimano has made the first change in their spline pattern since the introduction of Hyperglide in the late '80s. Dura-Ace 10 freehubs have taller splines than other Shimano models. As a result, it is not possible to install cassettes other than 10-speed models on Dura-Ace 7800 hubs. It is not, however necessary to use Dura-Ace 10 speed cassettes. The Ultegra 10 speed cassettes also accommodate the taller splines of the 7800 hu

That article answered your question ;

'The 10-speed cassettes will fit on any Shimano 8- or 9-speed Freehub with no problems.' Although I believe there is a spacer you require.

10sp cassettes work fine on all 8 or 9 sp Hyperglide freehubs, just need a 10sp cassette, it includes the spacer for 8/9 hubs

Doh. I am illiterate.