Tempura is rice flour. Rice has no gluten. Tempura is not Americanized, it is traditional.
Quit worrying so much, you'll raise your cortisol levels c:
Side note: the danger of tempura flakes is the omega 6-rich oils in which it is fried.
EDIT: Looks like I'm wrong about tempura: it's poison after all! At least the preparation seems to attempt not to activate the gluten. I wonder: does this change the body's reaction to gliaden in any way?