The waitress understood gluten free and even checked with the chef that the crepe appetizer I wanted was made with rice flour. Their pho (and the chicken soup I ordered) are gluten free. My fiance had a different soup that had thicker noodles that were not. I have never been to a Vietnamese place before were I felt confident that they truly understood gluten allergies.
All this being said, I do not have strong nor immediate reactions when I do eat gluten. It's more of a general inflammation and foggy feeling over time.