AOLserver 4.x does have built in virtual hosting but it is not as flexible as nsunix. The main disadvantage is that you can not (re)start individual virtual servers. You can only restart the AOLserver process affecting all virtual servers.
You can however start the AOLserver process with one of the virtual servers (instead of all virtual servers). Don't confuse this with starting individual virtual servers one after another. That is NOT possible.
For these reasons, I've switched to nsvhr TCP/IP based virtual hosting. I plan to write an article about my virtual hosting research.
Drop me a line should you want to give AOLserver 4.x built virtual hosting a try, and I'll send you a sample config file.