Yes I discovered it is true ! I have smoked dmt in a dream and had the effects come on, just as they would when awake, but it was a 'low dose' I was dreaming about smoking (10-15 mg), with total body-effects and some visuals. My dream was like my first attempts at breaking through, I was reliving that.
I hadn't expected it would be so obviously, 'just the same' as when awake - but it was . The body-load and the "oh oh, here it comes" feeling were there, and the visuals were slight, but still enticing and rich.