I would look really hard at whether you're actually running the version that you recompiled. It sounds like you are still running the old version to me. Maybe you did not copy the new binaries to the correct location?
AFAICT the ServerSignature and ServerTokens directives control whether the various parts of the banner are generated, but not their contents; the contents are determined by what's actually running. So if it is saying that you are still running OpenSSL/0.9.8k, then OpenSSL/0.9.8k is still compiled in.
Edit: One possibility -- if you built/installed from generic sources, the default installation location may not be where AIX expects!
Nostalgia isn't what it used to be.