I think that Fellay is not a freemason, but is tainted with liberalism. If he was a freemason, I think he would have come to a deal with Rome (and soon after have the society destroyed) years ago. I am sure he has had many opportunities to do so.
You know, Matto, it's the same logic that many Sedevacantists hold about the Pope.
"He's doing the Freemasons' work, therefore he's probably a Freemason."
On the contrary, I would suggest:
"He's doing the Freemason's work, therefore he's probably NOT a Freemason."
It's much better for the Freemasons if they have willing dupes carrying out their program WITHOUT them being card-carrying members.
Whether it's the head of the Church, or the head of the SSPX. Their goal is usually to form everyone with their own principles.
To rely on members exclusively is much more LIMITING than a broad re-formation of society, its philosophy, thinking, culture, etc. so it's in line with Freemasonic principles and ideals.
Think of it like a twisted version of "Love, and then do what thou wilt." If the love of God directs your actions, you pretty much can do whatever you "want" because it will all be for the love of God. A person who loves God would never "want" to offend him by sin. So whether he "wants" to feed a poor man, or pray some extra prayers, or admonish a sinner, or visit a sick person -- it doesn't matter. They can do whatever.
Likewise, "Think like a Freemason, and then do what thou wilt." works for the Freemasons. They are content to not "own" everyone, as long as everyone thinks like they do.