Does Embrace of Gonk Stack with druid cat form?
I believe so. I saw another feral druid with the buff who was running faster than i was without the buff.
I can confirm that it does. I have a speed set that I have up to 192% speed (including gonk) just running around (no speed increasing cooldowns used). It will be more once I get rank 3 of the ripple in space essence (minor is a 5% movement speed that stacks at rank 3).
If you are into this sort of thing then I recommend the monkey speed add on. It will tell you your current speed and it is easy to test if different movement speed items/enchants stack or not.