I agree with the need to use ADS entries verbatim.
It looks like the pybtex folks plane sphinxcontrib-bibtex for this (https://bitbucket.org/pybtex-devs/pybtex/issues/65/percent-sign-in-url-field-raises-an) and sphinxcontrib-bibtex points to latexcodec (http://sphinxcontrib-bibtex.readthedocs.io/en/latest/usage.html#encoding-percent-signs). Maybe we can PR a fix to latexdoc?
The immediate ways forward for this ticket at are:
1. Accept manual patches to the bibtex to escape %, or
2. Don't automatically populate lsst-bibtex bibliographies in Sphinx technotes and instead recommend that bibliographies be curated separately in each technote.
I'm hoping to do 1, but will be happy to do 2 to ship this ticket.