Answer 1
Current NUT codebase (since v2.8.0) is regularly tested with GNU, BSD and
Sun implementations of make, so seeing failures in release snapshots
(or iterations that made it to the master branch) is very surprising.
Please raise an issue on GitHub.
Answer 2
Older NUT codebase (release tarballs) has some hidden dependencies on
GNU Make which show up while running make distcheck. If you are running
make distcheck or its variants, you will need to install GNU Make
(devel/gmake in the ports tree), which is incidentally what the
official FreeBSD port of NUT does for all builds.