Wait a minute, I just read a scholarly rabbinic article which makes it abundantly clear that Gentiles may NOT partake of the Seder. Indeed any food added to the Seder pot makes the entire meal unclean as it violates the instructions given by G-d to Moses in the Torah. No thinking Jew should have been there. IN accordance with the text of Torah, they sinned in being there. Check the Exodus passage.
from the article: Matzah balls at the White House: Obama hosts third Passover seder