The NEC does not require GFCI protection of fixtures over tub or shower enclosures but if the fixture manufacture requires protection then you must provide it.
You say that many manufactures require GFCI protection? I have never seen this requirement on any fixtures other than fans.
I almost always provide GFCI protection in tub and shower enclosures for fixtures regardless of whether or not the manufacturer requires it. I do so most often using the execption you mention.