I'm running a variant of that. SM dual-head jbod with 2 linux servers. One is minimal config as secondary. Haven't had a failure yet, just switching to secondary when primary needs a reboot due to OS update.
Dunno about bhyve, but proxmox does the VMDKs as zvols. Maybe that sucks, performance-wise? Although 2 minutes sounds like a lot. Is this done at the CLI? I haven't used proxmox for quite awhile, but I'm wondering if they are not doing zfs snapshots, but something else?