FreeNAS 8.0 through 8.2 uses v15, and 8.3.0 and 8.3.1 uses v28. FreeNAS 9 uses v5000. I've played with the ZFSonLinux project (note that this is not the ZFS4Linux you mentioned) but it v5000 systems should be backwards compatible with everything FreeNAS 8 supports. I'm not sure about ZFSonLinux's support for partitioned zpool vdev devices though. Some ZFS implementations run on an unpartitioned disk, some don't. I can't remember if ZFSonLinux requires a particular design or not. I have never tried to use a zpool from FreeNAS on ZFS4Linux.
Considering all of your other problems I'd shy away from trying ZFSonLinux or ZFS4Linux until your zpool is fixed. ZFSonLinux just hit "stable" status a few months ago according to the developers, so I wouldn't trust it completely on a broken zpool. ZFSonLinux has had some major growing pains during development so there's a possibility of making things much worse.
