Again, the Resistance is a very loosely-knit group that doesn't necessarily have officially-published positions on various theological issues. So, for instance, Fr. Chazal's theological approach to the pope problem differs from that of most others. I do know that a priest who taught at the SSPX seminary in Winona believed in the necessity of explicit faith in the Holy Trinity for salvation and was reportedly admonished by Bishop Wiliamson for getting a little too close to "Feeneyism". I only heard this second hand though.