I'm not sure I understand your question. You don't need to tackle the gargoyles to get the first battlefield key. It's in the room before the gargoyles, so you have immediate access.
Once you touch the key, you'll have it for the rest of the act. This means that you can select secondary skills, and choose to travel there from anywhere else in Samuel's dungeons. That first key will only grant you access to the first battlefield dungeon; however, you'll be able to roam around the entire Act I battlefield, selling items, stealing items, and leaving stuff on the ground so it doesn't encumber your team. Just remember to pick it all up before you exit Act I in the real game, or you'll lose whatever's left behind.
Hope that helps. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />
