The vinegar test is pretty unreliable, and often gives false-negatives.
If it's actually marble (not ceramic with a marble pattern, granite, or something else), it will affect the pH. Maybe not quite as bad under the substrate, but marble is pretty much entirely carbonate. This dissolves into the water and raises your KH (maybe GH as well), and the carbonates react with any acids, and end up raising the pH of the water.
Slate is pretty reliable, people have used it for years, it's a silicate rock, so it won't affect water parameters, and it's relatively easy to drill (I've done it once with a regular high speed bit (that I never used again...))