fyi - adding the dll as a reference did not work. we ended up adding the AjaxMin dll and exes to the repository, creating a manifest.xml, then adding the following as a pre-build step:
"$(SolutionDir)\libraries\AjaxMin" -clobber -xml "$(ProjectDir)\AjaxMin\manifest.xml"
we also added the minified files to the repository so they are copied to the publish area. not the most elegant solution, but it works for our situation.