Was it ever explained how dreaming people in the dream bubbles could bring out physical items like the ring and people like Aranea once she resurrected herself?

The Ring is a Juju, it has some bizarre properties. In-Universe, Jujus are notorious for being weird, appearing and disappearing at random and kind of not having a set beginning or end, so being able to travel in and out of the Bubbles through dreaming and resurrected people only adds to that. On a more Meta level, Jujus kind of work like Plot Devices, so it’d make sense that they’d move the plot along with something as convenient as that.