I wouldnt say "unlimited" per se - it all depends on what they are doing. Employee interface users also use resources. You have to keep an eye on the webengine memory usage etc. I wouldnt let any webengine go over 300 total including both analyst and employee sessions.
What you can do is create multiple domsrvr-webengine sets on each app server, but then you need a web director on each app server to divvy up the load across its domsrvr-webengine sets. So what you would have is a load balancer divvying up the load between app servers, then a web director on each app server divvying up the load across its own webengines. Truly distributed at that point
Hope this helps,
Jon