Even if there is no viable conservative third party in 2008, it is a mistake to think that evangelicals will turn out for Giuliani. Look at the 1996 results, and remember that Dole, unlike Giuliani, was pro-life. However, it is possible that the New Yorker can win without much evangelical support.
I agree that the Democrats have little hope in the lower South, TX, and the Plains States, where Giuliani will win, though probably with lower margins than Bush had. Ditto for the Rocky Mountain states, except for NM and maybe NV and CO, where the Hispanic vote may tilt the states into the Democratic column.
However, picking up PA, NJ, DE, ME, NH, and CT would more than offset defections in the upper South and Border states. The Democratic margins in NY, VT, MA, DC, and MD are probably ironclad. I don't see much change in the Midwest, except for IA, where evangelical dissatisfaction would erase Bush's razor-thin (<1%) margin in 2004.
The bellwether states of FL and OH may be a wash. In FL, retired Yankees in south Florida may well offset disaffected evangelicals in north Florida and the Panhandle. Ditto for OH, where lost evangelical voters in southern and central Ohio may be offset by strength in the Cleveland and Akron areas, which are more Northeastern than Midwestern in outlook. The key to a Giuliani victory is CA, where Giuliani's political profile is similar to that of Schwarzenegger. However, the Republican Party will have to commit to huge media expenditures in very expensive markets to have a fighting chance in that state.
Hillary will not win FL, KY or WV no matter how many third parties there are.
69.4% of FReepers say they would vote Rudy if he was running against Hillary. This is BY FAR the most conservative group around and such a number indicates a LANDSLIDE for Rudy if that high a proportion of the MOST conservative people would vote for him.
Since you agree Hillary would have little chance in the South (where evangelicals and social conservatives are most concentrated) it does not follow that she would benefit from their hypothesized disaffection in states where they are not as plentiful.