The term "heath" is typically used to refer to an area of open uncultivated land, often characterized by low shrubs and vegetation, particularly in regions with poor soil and acidic conditions. "Heath vegetation" is a more specific term that emphasizes the type of plant life found in such areas.
Both terms can be correct depending on the context. If you are referring to the type of ecosystem or habitat, "heath" is sufficient. If you want to emphasize the plant life specifically, you might choose "heath vegetation."