I certainly agree with Yglesias that "It would be a big, big problem for Giuliani's general election campaign to have any of the major cultural conservative institutions backing a third party candidate. It's generally very difficult to win when you have a spoiler trying to take you down the way Ross Perot was gunning for H.W. Bush in '92 or Ralph Nader was taking aim at Gore in 2000." (It's particularly important that such a campaign would be primarily an anti-Giuliani campaign, just as electing Bush was the primary purpose of Nader's campaign.)
One has to question, however, whether or not this is a serious threat. My default assumption that Christian conservatives, in Michael Tomasky's phrase, "are far smarter than these left-wing lions of ideological chastity." I think this is pretty clearly an attempt to stop Giuliani in the primaries rather than an actual effort to field a third-party candidate. One reason that Nader and his followers didn't worry about the Democratic primary is that they're essentially unappeasable unless the Democrats were willing to commit electoral suicide; any Democratic candidate capable of winning more than 75 electoral votes would be unacceptable, so there was no reason to bother. Dobson, on the other hand, would accept any major candidate other than Giuliani without even a sniff of a third-party run, and he's trying to assure that it happens.
I still think that Giuliani will not be the nominee. If push came to shove, though -- granting that a pro-choice Republican winning would be a disaster for the forced pregnancy minority -- I'm pretty sure that Dobson will not be indifferent about whether Giuliani or Clinton makes at least the next four years of federal judicial appointments.