Glosslip makes a lot of conjectures as to whether the Church of Scientology has a hand in the troubles between JLO and Mark Anthony. I won't comment about that, but what I learned from this article was that JLO and Mark Anthony may have taken some Scientology courses back in 2006. Mostly Mark Anthony, though, but then we also learn that JLO's father may have been a Scientologist for the last 20 years.
If they really took courses, the CoS would probably count them in their "8 millions" members, since it seems they count anybody who once did a course in such an improbable statistic, but the question really is whether JLO and Mark Anthony are now ex-Scientologists (having dabled in for a while then stopped), or still closet Scientologists, or if they are somewhere in between.
The fact that Leah Remini, a celebrity Scientologist, is one of JLO best friends, and Tom Cruise a close friend of Mark Anthony, is of course not enough on its own to make of them Scientologists.