Generally heavy cannabis users don't dream as often or vividly as normal. One of the primary symptoms of cannabis withdrawal is extremely vivid dreams. I don't know if there's been any formal studies on this in particular, but I've heard enough independent anecdotes, that I'm convinced there is some relation.

Above was just the subjective part, there have been studies on the objective effects of cannabis on REM sleep, where it appears to decrease total REM sleep duration.

As far as the implications of this go, your guess is as good as mine.