I wasn't doing swinging back in the 90s. That was before my prime. Though I did know and hear about lots of sex parties.
Silk, which later became Bliss-out (after owner change) was considered interracial. But I only knew about them since 2006.
Japanese clubs are often NOT racist in the Western "White" conventional sense or manner. In the West, racist often believe they are superior to others races and can resort to extreme violence like murder, in additional to institutional discrimination. Many racist can't restrain their dislike for all other races/peoples they feel superior to.
The Japanese are often ultra-nationalistic or xenophobic. That means they might discriminate even against other Asians, because they believe their CULTURE (not race) is superior or they have excessive fear and paranoia about other nationalities.
The difference is that many Japanese don't mind sexual interactions or being around other races, especially if they can speak Japanese. Most Japanese, even if they dislike a group, can at least be outwardly polite or reasonably peaceful.
Most Japanese Happening bars don't have a race based policy, but a Japanese language speaking policy. Which is in place to avoid misunderstandings and confrontations. You might can get around such language policies, if you have friends that are Japanese or speak Japanese, and help get membership.
If you have problems in a happening bar in Japan, it's often more basic than racism, and is often about peer/group pressure. Fear of being seen doing something different from what other Japanese are doing, irrational fears over anything unknown, and fear of making an embarrassing mistake in the interaction.