Yes, but note that neither the Linux foundation nor OpenZFS are going to put themselves in legal risk on the word of a stack exchange comment, no matter who it’s from. Even if their legal teams all have no issue, Oracle has a reputation for being litigious and the fact that they haven’t resolved the issue once and for all despite the fact they could suggest they’re keeping the possibility of litigation in their back pocket (regardless of if such a case would have merit).

Canonical has said they don’t think there is an issue and put their money where their mouth was, but they are one of very few to do so.

The question was “How do you define GPL compatible?”. The answer to that question has nothing to do with code being split between files. Two licenses are incompatible if they can’t both apply at the same time to the same thing.