Material heretics (caveat: 'material heretic' is understood in different ways) may have the Catholic Faith, and it is not up to me to judge!
Here a more helpful approach:
Manifest material heretics just like manifest formal heretics do not (outwardly) profess the Catholic Faith and therefore don't belong to (the body of) the Church. That's independent of the specific definition of the distiction between material vs. formal heretic.
Occult material heretics just like occult formal heretics do (outwardly) profess the Catholic Faith and therefore do belong to (the body of) the Church.
Since we're not able to read hearts, we can't judge whether s.o. is or is not an occult heretic. On the other hand we can judge whether s.o. is or is not a manifest heretic, and we should do so where necessary to avoid false Gospels and sacrilege.
Manifest heretics can't belong to (the body of) the Church, since the Church visibly (and audibly) professes one Faith.