You can use both on the same directory. That’s how I do it for projects that I have put in the Appstore. Works well, but so far I always assumed I had to commit to both separately (not necessarily always both). So I would say: no, not possible. But looking around on the internet, it seems possible: https://www.belatrixsf.com/blog/a-happy-way-to-combine-svn-and-git
The Mendix Team Server is at https://teamserver.sprintr.com/ and is a regular Subversion server. You should be able to commit to it using any svn client and your (Sprintr) credentials. Be aware though, that a regular svn client will not set extra information like changed documents or Modeler version in the svn properties like the Modeler does.