By validity, do you mean, for example, if they would be considered violating the Mitsvos Bnei Noach if they engage in adultery – OR – by validity, do you mean if one of them converts to Judaism do they need they need a divorce for the non-Jewish spouse before they can marry a Jew .
I believe the answer to the first example is “yes” but Jewish never would have to deal with adultery cases involving non-Jews, and to the second I believe the answer is a female convert does need need any form of divorce from the non-Jewish spouse to marry a Jew (according to halacha, though Dina Malchusa Dina becomes an issue in some cases).