iRule or Custom Monitor that can be applied to a Server Pool, which can enable and disable an individual web site on a per server basis?

If I understand, Sharepoint servers host multiple web sites, and you want to disable pool member for a web site on the server but not others.

To do that, create as many pool as websites with same pool members.

Then create a custom monitor for every website.

Finally, create a ltm policy to forward to right pool based on hostname!