1. Can you have a tiki on one server w/ read only access to the db? No tiki users will ever login from this box. And have another tiki on another server w/ read/write acces on another server (admin box)? Will that work?
Yes, you can if you remove the authentican modules from the read only codebase. You would have a ultimate secure read only site.
2. Can multiple tikis run on a multiple web servers and use the same database?
Yes if you store the session data in the database you can actually do some cool load balancing.
3. What happens to tiki when it can't connected to the database, will the cache be serviced to the web client?
As sylvie says you get a rather poop error message, but its rather easy for a apache hack, to get a nice mysql restart or even a we are busy. This can maybe be used with the server load monitoring found on the Admin->General section.
4. Is it possible to have two or more versions of the same page/wikipage/article? That way one is consider production, second is stage/qa?
I believe mose has this coming in 1.10 release.