NetBSD ZFS has rather severe bugs, was this addressed by bitrig? They have remained unfixed in NetBSD for quite some years now.
Known Bugs
vnode reclaiming deadlocks
vnode fsync bug
kmem_cache_alloc/ aka pool_cache_get panics
Should also be noted that dtrace and zfs can never be actually integrated into OpenBSD due to them refusing to import CDDL licensed code.