It's not harmful in an immediate sense and many states have regulations prohibiting the use of CYA in commercial/public indoor pools (as well as spas), but having 2 ppm FC with no CYA will have an active chlorine level that is about 20 times higher than the typical outdoor residential pool with an FC that is around 10% of the CYA level. CYA doesn't just protect chlorine from sunlight, but hugely reduces the active chlorine (hypochlorous acid) concentration.
Though the German DIN 19643 standard when using ozone has the FC range be from 0.2 to 0.5 ppm with no CYA, it is very hard to maintain a 0.2 ppm FC level consistently, especially without automated dosing. So I wouldn't try that.
The problem is that with an indoor pool without sunlight you often need some form of supplemental oxidation, be it UV, ozone, or use of non-chlorine shock.
My wife has experienced this difference between an indoor pool with 1-2 ppm FC and no CYA where her swimsuits degrade (elasticity gets shot) after a single winter season and her skin is flakier and hair frizzier while in our own outdoor pool with 3-6 ppm FC and 40 ppm CYA the swimsuits last for years with minimal sign of wear and her skin and hair are not as adversely affected. This is most likely due to the indoor pool having 10-20 times the active chlorine level of our outdoor pool.
If you do decide to use some CYA in the indoor pool, don't overdo it. Use a small amount, say no more than 20 ppm, and then have your FC in the 2-4 ppm range and see how that works for you. If you find a buildup of Combined Chlorine (CC) over time, then you can use non-chlorine shock (MPS) every once in a while to get rid of organics (mostly urea) that aren't dealt with as quickly without exposure to sunlight.