You can use the same keyfile/certfile combination with both AOLserver (nsssl(e).so or nsopenssl.so) and Apache-SSL. I've never used mod_ssl, so I don't know if it'll work, but maybe someone else will chime in.
With Apache-SSL, both the key and certificate need to be in one concatenated file; as you probably know, they need to be separate in the case of AOLserver.
I've only tried this with a self-signed certificate, but it works fine.
