If the recessed light is listed as damp, there is no restriction for the installation in regards to height over/within the tub Zone, as long as it is not subject to shower spray.
If the recessed light is listed for wet locations, there is no restriction for height, within the tub Zone.
Example - can an typical flood lamp and luminaire (that we see installed outdoors) be installed directly below a shower head in the bathtub enclosure?
The general requirements for GFCI protection for personnel, can be found in 210.8(A) & (B). There are a few other locations in the NEC such as healthcare, and pools. These requirements are mostly for receptacles, except you will need to pay close attention to pools, as they are more restrictive than just receptacles.
So, when it comes to lighting and equipment, we are generally looking to the manufacturer for guidance. They will have the requirement for GFCI protection for personnel in the instructions if they deem it necessary.