According to the transcripts that form of the word was not used by any of them at any time during the debate. Granted, the level of grammar usage was not at a scholarly level at all times by any of them.
http://abcnews.go.com/print?id=4092530
Democrat Debate transcript shows that any form of the word regard was used only once the entire night.
OBAMA: ... is that, regardless of what the Republican candidates are talking about, I think that there are a whole host of Republicans ...
http://abcnews.go.com/print?id=4091645
Republican Debate transcripts show the following four uses of any form of the word "regard"
ROMNEY: But let's step back with regards to the president.
ROMNEY: ...On the same day the president announced the surge, I also, having spoken that day with Fred Kagan, who's one of the brilliant theorists in this regard, ...
ROMNEY: ... But with regards to those already here, it is simply not right and unfair to say they're going to all get to stay, ...
THOMPSON: ... I mean, it's essentially a national security issue, as well as an issue of fairness, as well as a social issue with regard to what states and communities have to face nowadays, ...