There should be a waterproofing system, though it doesn't necessarily need to be Redguard. Our local code requires waterproofing up to 6', I think, though I would go at least as high as the shower head assuming this is a shower over tub. You could ask them what the waterproofing will be if not Redguard. If the answer is that it's not needed, then you need a new contractor.

Waterproofing is always required anywhere you do not want water damage in a wet area. Redguard is the lowest of the low for waterproofing. Sorta like the Checkers hamburger of the waterproofing world. Anyone who knows better, does better. And those who don’t, don’t do it right.

The number of tile-related issues reported on houzz.com is evidence that tile contractors should be licensed as a specialty the same way plumbers and electricians are. Municipalities should also inspect all tile substrates and shower pans prior to tile installation. Both will go along way toward protecting homeowners against the consequences of a bad waterproofing job.

Kimberly:

The substrate and/or waterproofing manufacturer's installation instructions should always be followed. You may use Schluter Kerdi to waterproof over drywall. GoBoard, a type of cement board, requires no additional waterproofing. These systems are superior to RedGuard.

Thank you all for your help! Will talk to my contractor today to get some clarity on this. Thanks!