At work we have a monolithic repo containing Java, Go, Python, etc, organized like this:

  Java //src/com/yext/..     
  Go   //gocode/src/yext/...

GOPATH is set //gocode. .gitignore allows us to track only our code under the GOPATH using this snippet:

  /gocode/bin/
  /gocode/pkg/
  /gocode/src/*/
  !/gocode/src/yext/

We use glock[1] to sync dependencies across the team, without having to check them in.

The whole thing works very well at 50 developers and ~100 dependencies.

[1] https://github.com/robfig/glock