Do you have the zfs-testing repo enabled in omv-extras? If you do, it uses 0.6.5.7 from the official zfs repos which may not compile with 4.7/4.8. If you don't have it enabled, the 0.6.5.8 packages from the Debian repos is used which might work with those kernels.
No i just checked. Only ZFS is enabled not the "testing" but apt--cache -policy zfs* only shows me versions 6.5.7-8