Apologies for the delay - just been busy upgrading to AOLServer 4.
I have been "lucky", in that my front end server has not had the same problem as I mentioned previously (pthread_create failed), even though it is running with the aolserver-3.3.1+ad13 version.
I also have a static website (does not use OpenACS software and does not connect to database) which runs with aolserver-3.3.1+ad13 and which was also giving me the pthread_create error. After commenting out the Database pool sections in the config.tcl file, I could start the static website without any errors.
I will probably use pound to replace the nsvhr/nsunix functionality. Judging from the other comments in this thread, this seems to be the best approach for http as well as https connections.