In general, we use the "Fleshy Biped Test" to determine who's a real person or not. Mannequins are bipeds, but not fleshy: not real. Vegetative-state hospital patients are fleshy bipeds: real.
As for Artificial Intelligence, it adheres to the more fundmental notion of the Turing Test. This stresses the importance of not confusing Fleshy Biped aspects when speaking about intelligence as an abstract idea. But the more important aspect about the test is captured in the joke:
Q: "are you getting smart with me?"
A: "if I were, how would YOU know?"
So what should a lucid dreamer use to determine a code of conduct in another world? Can you do anything you want, so long as you don't make the mistake of waking up and repeating that behavior?
As far as I'm concerned, I do the best I can to treat dream beings as real beings at some level. I tend to only attack when attacked, and I'm even cutting back on that instinct. I definitely would not do something "physically harmful" to something in a dream if it treated me intelligently and was not bothering me. Maybe I've missed out on the thrill of skeet-shooting kittens, but that's kind of o.k. with me for now.