Ok, since my fellow ex-seminarians utterly failed to answer this question for you, I will:
DE FACTO the Resistance does have a position on this. Priests from the Novus Ordo are to be conditionally re-ordained. And the Resistance only makes use of known good or "certainly valid" bishops -- such as +Lefebvre-line.
All priests working in the Resistance are either conditionally ordained by a +Lefebvre line bishop, or they were already ordained by one in the SSPX.
Seems pretty straightforward to me. Classic SSPX position, once again.
Is that really the Classic SSPX position? We know of NO priests that were not conditionally ordained even during +Lefebvre timeline. Also, I personally know of an NO priest, who was conditionally ordained by +Williamson, even though there was no positive doubt and it was done because people complained.
If the Resistance require conditional ordination, how does that apply to Francis? If there is a sacramental theological reason to doubt all NO priests, then we could easily come to the conclusion that Francis is at best a deacon or worst a layman.
Side note concerning conditional sacraments: I have been finding that more protestant converts to NO church never had their protestant baptism investigated. And as they move to tradition, the neo-SSPX does not investigate it either.