I don't honestly know. Perhaps they are not sedevacantists. I was right next to one of their churches in Ridgefield, CT, for a number of years, but I confess I haven't followed them much in recent years.
Having previously been in the SSPX for a while, I can attest to the following:
The SSPX has never been sedvacantist. The SSPX regularly prays for the Pope, inserting his name where applicable.
Individual priests are known to be "closet" sedevacantists, but they do not discuss it. However, in one case I have seen, a priest subtely revealed his position since he never invoked the name of the Pope by name when it came to time to pray for the Pope. He would say, "Let's pray for the Holy See" and then use one of the prayers which do not require the insertion of the Pope's name. But these types are in the the very small minority.