No, it is not. Since you were using the water and ship metaphor. Think of it like this - the sea is the Nether. The Ship (that is leaking) is Outland. The air is Great Dark Beyond / physical universe / reality. That's how Outland is. It's floating on top of water, partly in the sea, and partly not. Stepping out of it far enough and you will fall into water, but the ship / Outland isn't under the sea / inside the Nether yet.
It was stated and implied multiple times in "Illidan" that Outland is still part of reality (the physical universe). The Nether exists outside of reality. If Outland is fully in the Nether, it shouldn't be part of reality any longer.