The commit log here is probably the thing to look at. I went through adding one file at a time and looking at docker stats and top on OS X to figure out what was spiking CPU. As of 1.12.0 it was the number of watched files. Adding more files added more CPU. As of Docker for Mac 17.03.1-ce-mac5 it appears to be resolved.
This was done with docker for mac 1.12.0
To test gulp
cd gulp
docker build .
# optionally name it with docker build -t gulper .
cd ../
docker run -it -P -v `pwd`:/code gulper "/bin/bash"
# now you're inside the container
mv /node_modules /code/gulp/node_modules
cd /code/gulp/
gulp watch
Open up Activity monitor on your mac and look at hyperkit CPU
Also run docker stats in another window to see it change.