Kristin at The Reyn Pho in Pasadena told me yesterday that they will indeed be open on Thanksgiving day for those that need to get their Pho on (my words, not hers). They open at 11am.
So, if you are not a turkey fan or just need a Pho fix, this is a great option.
The Reyn Pho
635 N Lake Ave (south of Orange Grove)
Pasadena, CA 91101