Smartmontools v7.4 and above supports NVMe testing using smartctl, below that and of course they do not, however using the nvme utilities that are native to FreeBSD and Linux, the self-tests run just fine. And even when smartmontools v7.4 is present, the TrueNAS GUI does not allow you to select NVMe drives to be tested. Once TrueNAS has this stuff worked out, I may remove this feature from the script as it should not be required anymore and it will reduce the number of options to make it a little less confusing.
Glad that worked for you.