Nope.
According to the
members list it is dl65, closely followed by Flame, closely followed by Corrosive then Techno (admin's alt account) all within around 2 hours.
However, the earliest registered member may be 2k_dummy, I remember him telling me he posted for a long time as a guest because the login system went belly-up for him or something.
Might need an older member to testify as to who was the first.
but it definitely wasn't GX, look at his profile and you'll see.