I'm familiar with Buchanan, of course, but he's always been a professional xenophobe. What I'd be more interested in seeing is the extent to which that basis for opposing abortion has actually taken root within the anti-abortion movement, at grassroots level and/or among the "leaders" of the movement.
Santorum, from what you've given me, sounds to me like just your basic nuclear family fetishist. We have an organisation here that uses various guises but is most infamously known as Youth Defence. They modeled themselves on Operation Rescue (except, with abortion being illegal here, there's nothing for them to rescue - a fact that I'm sure is a source of some regret to them) and can be counted on to get involved in every "moral" controversy that arises albeit under a different name each time. They've fought the introduction of civil unions (so far successfully) as the Mother and Child Campaign; they've invented local "residents' groups" to oppose sex clubs; they're now gearing up to oppose a possible constitutional amendment on children's rights under the name Parents for Children. You name it, and if it can be seen to undermine the patriarchal family structure they're against it. Of course it's not difficult to draw a connection between that view and anti-immigrationism, and in fact a former leader of Youth Defence has spoken on a platform with European neo-nazis while some of the group's founders have links to the more racially-purist elements of Irish "republicanism" (really nationalism where these people are concerned). But I'd be inclined to see the "family" obsession as the core of this philosophy with racism deriving as a consequence of it, rather than the other way around.