According to GB you can freely choose what action skill and pet you want to use, until you realize you can’t upgrade either if you spec in the wrong tree. I just tried out the skill tree and chose the jabber and the rykk/rakk pet and action skill. I focused on the pet tree under the skag pet and after unlocking relevant tiers tried to upgrade the pet and action skill under a different tree, only to find out I couldn’t.
Am I missing something like maybe a level toggle to allow the upgrade of the respective pet and action skill augments? I am seriously hoping they did not make the claim of freely utilizing the combo you want to only require you to place points in their respective trees to unlock the appropriate augments. I am hoping they are level gated and not tree gated.