This depends entirely on what being a Thelemic Magician means to you and how you interpret it. Thelemites usually follow Scientific Illuminism, and it is possible to interpret that philosophy in a way that is non-supernaturalist and is in line with scientific and evidence-based belief.

However, Scientific Illuminism does not require atheism, anti-supernaturalism, or adherence to scientific belief. So the answer to this question goes back to whether or not you agree with the Seven Tenets, including the idea that beliefs should conform to our best scientific understanding.