How to see / capture ALL SMB server log output in 10.12 and 10.13?
While I have not yet found the actual solution to the original question (I will update this once I do or someone else does) I did find a solution it seems for the actual problem that was leading me to ask this question.

It appears that macOS 10.13.x is severely problematic with its SMB server. Windows clients seem to connect fine, but 10.13 clients very, very frequently have severe hanging issues. I have now also seen others mentioning this problem for some months.

The trick appears to be to modify /etc/nsmb.conf such that it changes the behavior a bit (I think the actual key being to change the protocol version to 1):

[default]
signing_required=no
dir_cache_off=yes
protocol_vers_map=1


After rebooting clients that I've updated to have this I now no longer experience the hangs that I previously had on several 10.13 workstations. Windows also still works fine accessing the shares. OpenZFS on OSX pool sharing is also great with this.