Whether a plan reimburses alternative medicine is governed by two mechanisms. The first is the scientific recognition clause, modeled on § 4 (6) MB/KK. Under this clause, the insurer pays for methods that are generally recognized by science. Beyond that, it pays for methods that have proven just as promising in practice, or that are used because no recognized method is available. Plans can make this clause stricter or extend it in favor of the policyholder. This is exactly where plan quality differs.
The second mechanism is the Hufeland directory, a catalog of naturopathic methods. Plans that refer to the Hufeland directory reimburse the methods listed there, for example acupuncture or methods of traditional Chinese medicine, even without proof of scientific recognition in the individual case. If you need treatment regularly, a plan with an explicit reference to the Hufeland directory is the most reliable basis.