<note: I'm much more familiar with linux systems than netBSD>

I can't speak to the nroff question, except try making a sym link to groff. 
Crazier things work.

tar syntax is normally:
tar -[txc] [z] [v] [f] tarfilename

t - test the archive
x - extract the archive
c - create a new archive
z - archive has been gzipped
v - verbose, spew files entering/leaving archive
f - file, the next argument is a tar filename.

Try tar -tvf blotz.tar or
tar -tzvf blotz.tar.gz

Hope this helps.

-Joe Johnston