Yes, the Vasudan textures on the Ra were there from retail, and even from FS1, for that matter. If you take a closer look, you'll notice the Vasudan at the rear window is mooning you.
Yes, Blaise's Derelict update uses Lightspeed's nebulae. The six links that Blaise posted on the first page of that thread still work fine for me.
To answer your final question, you probably won't see anything new about 3.6.7 just by playing through it. A lot of the new features in it, including a lot of bugfixes, don't change the normal gameplay experience. If you take a look at the new launcher, however, it has improved mod support. When the next set of Media VPs is released, you'll definitely see some changes, including a few new HTL-ified ship models and the new 3D shockwaves.