Hm I used it once for a room so I could understand how a cerian perspective would work, and i drew ontop of a screenshot i took (of the room i modled)
but it is.. not cheating
this goes right back to the timeless argument (mainly coming from very young inexperienced aritsts) that references are evil and we should do everything from our minds
3d is just another tool we can use to our advantage. personally, i find that seeing obviously 3d items and backgrounds (ones that haven't been drawn ontop of in any way) can kind of throw me out of the story becuase they're so blatantly different from the art style used with the characters? but i definitly don't think it's wrong, i can completely understand how, in order to get those X pages a week, sometimes shortcuts need to be made, and background work is without a doubt a big, big time spender.
it's really weird honestly because so many times you see people praise works and artists for amazing background work (for example, Kengo Hanazawa)
when in fact.. the backgrounds in those works are just photoshop-edits of real photos they took and digitalized.
same goes for shoujo manga that's been using screentones instead of manually drawing their backgrounds for.. ever
people have been using "shortcuts" to do backgrounds since the beggining of popularized comics, and people have been using references to draw since the beggining of time itself, just because it's a bit more visually clear now doesn't make it less legitimate. it's the creator's choice if they want to make it more or less obvious, but in terms of Telling The Reader because it's Cheating?
Nah.
*sidenote, legally and potentialy ethically speaking, if you're using someone else's works (you didn't model the 3D room, or you're using photos someone else took without their permission,) that's a whole other animal which can bring up a lot of disscussion too!