It's always an interesting questions, and in a lot of ways how much control your game dev team has over the world-state is a deciding factor on how much interactions your devs should have with the world, if you ask me. In a static game world, a dev from your content team just shouldn't be playing with players - they know way too much about things that can affect your play experience directly. In a world where you physically place every enemy, you'll never be surprised by what's around the corner and just that fact alone will influence other players near you. For this reason, we had pretty strict ideas of what was "right" for a dev to do on Auto Assault. Generally if you played at all, you had to play in a way that would never draw attention to yourself, which meant casual play, essentially.
Likewise, the dev's intended roll in ongoing content plays into what a dev should and shouldn't do in your game world. In both Rift and another project I was working on called Revival, the devs were meant to actively play the parts of key characters in the world, not as players, but as intelligent NPCs. Sort of like what Lady Grace is suggesting with her Yoru king idea. The "Live team" was as much a troupe of performers as they were a group of developers. This meant a high degree of intended interaction with players, but never on equal footing. In fact in both games, originally, playing as a player was off the table for the team. I don't know if that carried through after launch for Rift since we made some pretty dramatic changes in its last year of pre-launch dev that threw that plan out the window, and I never played it as a player after launch, though.
However, with a few exceptions, neither constraint or concern really applies all that much to Chronicles of Elyria. One the one hand, the content team has almost no responsibility for the state of the world - that's managed actively by the game systems and those game systems operate on so many inputs that any single player's actions, not matter how informed, aren't going significantly disruptive. And on the other, our team (again barring a few exceptions) won't be playing key roles as non-players in the world. We put so much stock into our focus on AI because the intent is for the game to not require that sort of activity from the team. We won't have a troupe of performers because we've built the game to not need one. And with the story engine not only generating new activities for everyone, but also deciding when and how those activities are introduced and executed in the world, the team isn't really involved and doesn't really have any more insight into "what will happen next" than any other player.
There are some exceptions - anyone working on the 10 year story will have some idea of the sorts of signs and portents that could precede major events for example - and so at least some of us won't be perfectly free no matter what, but in theory our group of devs should have more freedom since the "safe decision space of play" is much broader for us.
Now, whether that means we'll allow everyone to do everything might not have anything to do with what's safe to do. There are business and community reasons to potentially dive in or stay out of the pool completely. But, mechanically, most of the reasons you'd want to keep your devs out of the pool don't really exist in CoE.
Hope that helps! :)