Hi!!
As far as I know Cloud ML was developed to work specifically with Tensorflow. They support several runtimes for TF versions up to 1.4, as well as specifying a “custom” TF version.
I have never heard that this service is available to other frameworks, however if you do manage to make it work do let me know how. It is a nice service and it would be great to use it with pytorch!
(However you could also always set up a VM with their compute engine and gpu’s to use pytorch)