Yes, I do think that after this happened the whites have stepped up and started to declare again that they are the dominant force on this planet, and that no one else comes close to being what they are, and to being what they can accomplish as a nation together.
Sadly, American has always had pockets of racists. Perhaps in the aftermath of the attacks they feel more comfortable being vocal, but it seems to me that racists and other bigots feel so confident in their beliefs that they openly push those judgments on others. The attacks probably increased fear in some people who would not otherwise be so racist, but I wouldn't necessarily term them white supremacists.
I do not think that there has been a rise of white supremacy in the United States due to 9/11. I think that situations like 9/11 will always give such groups a reason to be more vocal than usual, but there isn't an epidemic of more of a support for such groups.
I believe after 9/11 the white supremacist groups just got a little louder. They never went away or went into hiding. The media was not focusing on them at the time. After 9/11 the media did start to focus on them more because of the anger towards Muslims. America wanted payback at the time, and so many people were hurt and angry which gave a perfect platform to the hate groups.
No, white supremacy has not been resurfacing in the United States of America after the attacks of 9/11, because people have been kinder and more loving than ever before. People cannot ignore the reality of 9/11, in that the attackers were of a specific race that attacked in the name of their religion. It is fair to acknowledge that fact, without being labeled a racist.