* AFAIK GFS is shipped in the kernel - i.e. you can create a GFS on top of a shared storage (which would that be in your case?).
* once you mount it you can add it as directory-type storage to PVE and be able to use it.
However - why would you want to use GFS - compared to e.g. shared LVM (which is used by more users and is thus better tested)?
I hope this helps!