The DNS server provides you service, not software. The free/proprietary
dichotomy does not apply to services. However SaaSS is a great threat to our
freedoms: https://www.gnu.org/philosophy/who-does-that-server-really-serve
But using somebody's else DNS server is not SaSS because maintaining the
ip-name mapping is not your "own computing".
You can run your own DNS server though. Or you can simply choose one that
does not lie (typically for censorship purpose) and does not represent a high
privacy risk (not Google's...). If you are in a country that does no ask its
Internet Providers to censor the Web (such as China or France or...), then
their DNS servers probably are OK.
