From the website:
The precompiled fonts are released under the terms of the GNU GPL
version 2, or (at your option) a later version, with the exception
that embedding the font in a document does not in itself bind that
document to the terms of the GPL.
So, it would be not legal to use GNU Unicode (including the fonts) on any closed-source application, per copyleft licensing terms.
But in your situation, I would strongly recommend that you make use of the open and permissive DejaVu ttf Fonts (http://dejavu-fonts.org) within a font rendering library under a permissive license, on your work.
However there's a GPL exception concerning the use of fonts, made for permitting the non-GPL compatible code to read and write documents and templates that embed the GNU font, as mentioned in the licensing terms:
These font files are licensed under the GNU General Public License,
either Version 2 or (at your option) a later version, with the
exception that embedding the font in a document does not in itself
constitute a violation of the GNU GPL.