Are there any fenton/mueller position sede bishops or priests?
Or does formal apostolicity flow through those who deny the salvation dogma?
Well, I do find it remarkable how much they love to quote Fenton or St. Thomas when attacking those who reject BoD (since they both believed in it), but then suddenly ignore them when it comes to whether or not explicit faith in the Holy Trinity and Incarnation are necessary for salvation (which they both believed).
There's no formal apostolicity anyway carried on by the "sede" bishops, since they all lack any kind of ordinary jurisdiction.
Nevertheless, regardless of what you think along those lines, the vast majority are probably not formally or pertinaciously heretical about their error. Many, for instance, believe what they believe because they THINK that Trent taught BoD. That's clearly not an improper formal motive for their belief. They're just mistaken. Basically, the litmus test for pretinacity has to do with imagining there's a Holy Traditional Pope, and hte then comes along and condemns BoD and forbids any discussion of the matter. I'm sure that the great majority of them would simply accept that due to Papal authority, meaning they were not pertinacious in their belief. Some, however, would claim that this Holy Pope is a heretical Feeneyite ... and simply declare the See vacant, illustrating the problem with straight SVism. You can reject any papal teaching by simply declaring the man who taught it to be an AntiPope.