My contractor used mold resistant drywall for ceiling in shower stall; ceiling will be tiled. The stall will be surrounded by frameless glass and there will be about 4" gap from ceiling and the glass. Should I tell contractor to replace drywall with cement board, or is mold resistant drywall fine in this case with liquid waterproofing on it? Cement board will be used for shower walls.
My shower was originally done entirely with drywall, not a scrap of cement board in sight. It was installed in 1976 by the then-owner of the house and lasted until around 2012 when someone stumbled in the shower and kicked the wall a little too hard.
Water falls down, well-done tile and caulking shouldn't let any water through regardless, drywall for the ceiling should be fine as long as you're not in the habit of taking hours-long hot, steamy showers with no vent fan. (in which case all of your drywall is likely to suffer, whether it's in the shower ceiling or not.)
But cement board is better, so if you're willing to pay for it, then by all means do that instead.
Last I looked cement board and drywall prices are low and comparable enough to not make a dent in your budget (looks like your ceiling is $10-20 of cement board at most, including screws). I did my first shower ceiling with cement board, it worked great.
As for isherwood's concerns about a thin layer of paper not holding the weight of tile, check out Schluter's Kerdi membrane. A thin layer of water proof orange membrane, mortared to that thin layer of paper, works amazingly well. I did my last project with it.
Drywall showers, as mentioned by Perkins, are known to mold because grout ages and cracks with time - even well done tile. I consider Perkins lucky the walls weren't covered in mold; not recommended.
I am a DIY guy, neither a contractor nor a professional nor do I have any affiliation with Schluter.