Q. Is a Jewish man permitted to seclude himself with a non-Jewish woman together with a non-Jewish man, or non-religious Jewish man?

A. Shulchan Aruch (E.H. 22: 2) mentions that Shamai and Hilel prohibited seclusion with a non-Jewish woman. Poskim disagree whether a Gentile or a non-religious man qualify as shomrim or watchers. Some are lenient (See Pischei Teshuva E.H. 22: 2, Shov Yaakov 2: 19, Erech Shai 5, Zechor Leavrohom 2: 10, Chazon Ish 35) while some are stringent (Noda Beyehuda 1: 69, Yam Shel Shlomo 21)
Horav Shlomo Miller’s Shlit”a opinion is that in need you can be lenient.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a