Darwinports GNOME and spell checking.
It doesn’t happen.
The DarwinPorts ports collection includes aspell, but not GtkSpell or GnomeSpell packages. So most of the Gnome software that supports spell checking apparently does not require it, and so I failed to notice that the software had no spell checking.
I guess I have a weekend project ahead of me making testable ports for GtkSpell and maybe GnomeSpell…