Just because you have a Makefile in your repository, it doesn't mean the package(s) aren't `go get`-able. As long as the package can be built with `go install`/`go build` it should be fine.
The authors example is clean/simple. Here's an example not so clean/simple example where we needed to do more complex stuff like build for all target platforms[1].
[1] https://github.com/cloudfoundry-community/stackdriver-tools/...