I have a question about WordPress and LDAP on a Unix platform, is the appropriate place for that Server Fault or here?
There isn't, exactly. Server Fault is:
so naturally there's lots of overlap. If it belongs on both you can pick which one you think you'll get a better answer on. In this case, I wouldn't expect WordPress to be particularly sysadmin-oriented, but SF has quite a few questions about it, and certainly LDAP is on-topic there. Setting up any app on Unix is likely to be on-topic for us, so your question is probably fine on either site