I dunno. The fact that Rockwell's term (1956?-1964) is counted as part of the Social Populist era suggests that he either was a Social Populist or agreed with some of their positions. Also, the POD takes place when Rockwell was a teenager, so there's no guarantee that same experiences that shaped his OTL views will take place ITTL.
You might very well think that, but I couldn't possibly comment.