The key with Dream is this:
Wounds and conditions don’t have any effect on the creature’s waking body and mind. Fantastic adventures don’t yield real treasure or experience to the waking being, though knowledge gained in the Dimension of Dreams occasionally aids in solving real challenges faced in the waking world. Even the worst nightmares hold little true danger for the dreamer. Should the lucid body die, the dreamer simply awakens, perhaps a bit shaken but otherwise little worse for the experience. A creature with the Lucid Dreamer feat awakens from such an experience fatigued, as her mind is more invested in perceptions of the dreamscape.
The general gist of it certainly supports the idea that nothing from Dream is supposed to make it back to the real world. Certainly, any inherent bonuses granted by wish don’t apply—those would fall under the category of “conditions” that “don’t have any effect on the creature’s waking body and mind.” Here, I am going to read “waking” to mean “outside of Dream,” but I’ll reconsider that interpretation in a bit.
That means that anything you try to take out of Dream—including stuff you try to project out of Dream with astral projection—simply don’t work because they were only dreams to begin with. Astral projection might be able to copy the dream of an artifact, but the copy wouldn’t be any more real than the “actual” artifact you created within Dream, and so... the implications on that are not clear, but a functional artifact does not seem to be within the realm of possible answers. An inert replica of it, a mere illusion of it, nothing at all, those all seem plausible—though since the rules don’t describe the interaction, we can’t know for sure and we’re getting well into houserule territory. But the point remains that you can’t take the artifact off Dream and expect it to still be the artifact that you dreamed up. That much seems clear; it’s whatever you have instead that is unclear.
But consider for a moment the alternative: that “waking” refers not to simply “being outside Dream,” but rather the more usual mundane sense of “not being asleep.” Well, then you have a problem because it’s your waking self within Dream. In that case, you might well not be able to affect yourself at all with impossible actions—because you aren’t dreaming even though you’re in Dream. You could still use impossible actions to alter Dream, but you couldn’t interact properly with the alterations you make. This gets really confusing and doesn’t seem to be what Ephemeral Tread is going for, but I point it out because I want to emphasize that this alternative interpretation still doesn’t really work for these purposes.
Of course, I’m coming at things from an a priori conclusion—that you can’t abuse Dream in this manner—and working to justify that, which is not the right way to handle these things. Your interpretation isn’t, that I can tell, clearly prevented by the text, though again the overall gist of the text, not to mention the general context in which we expect a balanced game, strongly suggests that it’s not supposed to work. There just isn’t really a clear, strong, objective RAW answer that we can give here.