de-Bazel-ing TensorFlow Serving
You are close, you need to update the environment as they do in this script
.../serving/bazel-bin/tensorflow_serving/example/mnist_export
I printed out the environment update, did it manually 
export PYTHONPATH=...
then I was able to import tensorflow_serving
While I admire, and am somewhat baffled by, the documentation's commitment to mediating everything related to TensorFlow Serving through Bazel, my understanding of it is tenuous at best. I'd like to minimize my interaction with it.
I'm implementing my own TF Serving server by adapting code from the Inception + TF Serving tutorial. I find the BUILD files intimidating enough as it is, and rather than slogging through a lengthy debugging process, I decided to simply edit BUILD to refer to the .cc file, in lieu of also building the python stuff which (as I understand it?) isn't strictly necessary.
However, my functional installation of TF Serving can't be imported into python. With normal TensorFlow you build a .whl file and install it that way; is there something similar you can do with TF Serving? That way I could keep the construction and exporting of models in the realm of the friendly python interactive shell rather than editing it, crossing all available fingers, building in bazel, and then /bazel-bin/path/running/whatever. 
Simply adding the directory to my PYTHONPATH has so far been unsuccessful. 
Thanks!