I don't see the advantage of passing through an NVMe.
From my findings your better off hosting VM's on them and using ahci-hd for the images versus -s 7:0,nvme,/dev/nda2
NVMe passthru on Bhyve findings
I am currently using a SuperMicro X10DRL board for my Bhyve Virtualization machine. OS boots from a 64GB DOM. I use two Samsung 512GB PM953 drives in a M.2 form factor mounted on a SuperMicro AOC-SLG3-2M2. The slot where the card is installed is set to x4x4 in the BIOS for bitfurication. I am...
forums.freebsd.org
From my findings your better off hosting VM's on them and using ahci-hd for the images versus -s 7:0,nvme,/dev/nda2