How to share directory over NFS from Mac? (w/o macOS Server app)
What was required was the following line in /etc/exports:

/path/to/shared/dir -mapall=&lt;uid of local user on host machine with correct perms&gt; -network 192.168.56.0 -mask 255.255.255.0


exports(5) is the FreeBSD version, obviously. Once I did some googling for the solution with respect to "FreeBSD" instead of "Mac", the necessary information presented itself, the a colleague pointed out the exact flag needed.

Source: http://www.freebsdmadeeasy.com/tutorials/freebsd/using-freebsd-nfs.php

NFS Manager was helpful in validating the solution but not necessary.