I don't see how the title "Black Ops" precludes this being set in the Second Indochina War a.k.a the Vietnam War. On the contrary, Vietnam has plenty of history as far as black operations are concerned.
Anyway, I will be paying close attention to this title. Considering the rather unique setting and the fact that Infinity Ward disappointed a lot of gamers with Modern Warfare 2 (especially PC ones), this is truly a unique chance for Treyarch to shine. If they can make an excellent title, it will help a lot in shaking off the stigma of them being the "B-team".
One can only hope they will not make the same mistakes as Infinity Ward....especially as far as mod support/dedicated servers are concerned.