Yes, it is possible to have Nested Windows machines in Google Cloud, as explains Microsoft in this documentation it is required an Intel processor with VT-x and EPT technology, and Google Cloud Platform has it.
In the following Google Cloud documentation does not appear any Windows VM as tested but I saw a lot of people using Windows Nested virtual machine in the Google Cloud.
For that, create the nested virtual machine IMAGE with the "licenses flag" as follow:
gcloud compute images create nested-vm-image \
--source-disk disk1 --source-disk-zone us-central1-b \
--licenses "https://www.googleapis.com/compute/v1/projects/vm-options/global/licenses/enable-vmx"
and then, create the virtual machine based in the previous image with at least a "Intel Haswell" CPU (or newer) as requirement:
gcloud compute instances create example-nested-vm --zone us-central1-b \
--min-cpu-platform "Intel Haswell" \
--image nested-vm-image