I have an application development server that is automatically updated every night with a massive shell script that we run with
make clean && make html
I was able to find the answer to this question here. The error message that is shown when you attempt to build the sphinx documentation from the root is as follows, and leads to the answer that was provided there:
Makefile:12: *** The 'sphinx-build' command was not found. Make sure you have Sphinx installed, then set the SPHINXBUILD environment variable to point to the full path of the 'sphinx-build' executable. Alternatively you can add the directory with the executable to your PATH. If you don't have Sphinx installed, grab it from http://sphinx-doc.org/. Stop.
The full command for anyone looking to build sphinx documentation through a cron when all tools are installed in various virtual environments are listed below. You can find the location of your python and sphinx-build commands by using
which while the environment is activated.
make html SPHINXBUILD='<virtualenv-path-to>/python <virtualenv-path-to>/sphinx-build'