I posted this in another comment, but during uni I did in fact write code in lucid dreams. A friend can vouch for a specific time when I woke up from sleep during an all nighter, to fix a very specific bug (which I just remembered, we didn't even know it existed), then went back to sleep. On another occasion, I designed a recursive path-finding algorithm to replace djikstra's algorithm, all in my sleep.

It definitely can be done (though I doubt it could be done consistently and without actually imagining shit up), but it really shouldn't be done, I really doubt I was really resting while doing that.