How to refer to someone who works at a hotel?

A general term is hospitality worker. This broadly refers to someone who works in the hospitality industry, which also include, for instance, restaurants.

In very broad strokes, hotels are part of the hospitality industry. In most cases this can stand alone without tagging "worker" or anything on.

Bob: What line of work are you in?
Alice: I work in hospitality.

If you need something more specific I would suggest using "hotel staff". This could cover virtually any non management role and is a bit more classy than "hotel worker" or similar.