Any evidence it messes with REM sleep in general? I usually feel groggy the morning after a night of weed. Like I didn't get enough sleep, even when I get my standard 8 hours.
I dunno if it messes with REM sleep or somehow otherwise impedes dream awareness. It'd be interesting to look into.
We approach lucidity (consciousness) as a dream becomes unrealistic. As we approach lucidity, first we see color in a dream. This knowledge alone can become a trigger for lucidity. If color doesn't wake ones consciousness, one might achieve consciousness while dreaming because of an obviously impossible event in the dream. Often, I'll finally snap into consciousness while dreaming by managing to say, in the dream, "hey, I'm dreaming". While lucid I've studied, edited my papers and other productive activities. I actually look at my paper, page by page, see errors, wake up and correct them. I'm not always productive, though. Mostly I just go swimming in exotic or bizarre locations (I'm not a fan of heights, or I'd fly more often).
There are monks that go directly into lucid dreams, maintain their conscious awareness and wake directly from lucidity (the time to enter and exit REM cannot be lucid because one's not dreaming). Aside from time into and out of REM, these monks never lose consciousness. They spend their entire lives aware of the world around them, exploring it and analyzing it and themselves.
The closer one gets to lucidity, the more one remembers about a dream. If someone remembers a dream vividly, they were very close to waking their consciousness while dreaming.
For more about lucid dreaming, I recommend Patricia Garfield's "Creative Dreaming".
Here's my theory (pulled from my 4th point of contact) about weed suppressing dream awareness:
Weed makes one more vulnerable to suggestion. One is less likely to call "BS" on ones own thoughts, notions or ideas. This could suppress the progress of ones consciousness to awareness in a dream. If one is not questioning the events of a dream, one will not arouse ones consciousness.
Or it could be a REM disruption thing, as you speculate.
Side note: It's unfortunate that most people's closest experience with lucid dreaming is when something terrible is happening in a dream and they say "I'm only dreaming, I can wake up". And they tear themselves from the dream, waking in a sweat. Most people have done that.