If you want to use UML only, you could use limited class diagrams - without m-n associations and methods. But if you are using some class-table mapping tools, you can use anything, except m-n relationships only.
Nobody had ever said that you can use Class diagram for OOP classes only. You can use them for any more or less formal concepts, if their needs can be covered by the complex of CD elements. I use class diagrams for UI planning and even formal text planning. And tables are very close to classes. So, no problem.
You can use data model diagrams, if you need something that is CALLED data diagram. But they are covered by class diagrams fully. That is the reason they are not supported anymore.
Your task is to make the model understandable for everybody, who can get it in hands. Class diagram is the most widely known UML diagram. A good title and a pair of comments will resolve all possible misunderstandings.