At this point in time there is a gap in the System Center 2012 Orchestrator documentation available which explains IIS requirements. Current SCOrch documentation is available at: http://www.microsoft.com/en-us/download/details.aspx?id=29258. The following blog article provides details on what components in the Web Server are required for Orchestrator 2012:
Question: What IIS features are required for Orchestrator?
Answer: The list of features required are listed below.
Both of these are single server installations with a remote single SQL Clustered backend:
This is a single server installation with a remote SQL 2008 R2 CU6 4 Instance backend
This is a Clustered SQL 2008 R2 CU6 server installation with a remote SQL backend
This is the previous Web Server (Installed) Role Options after allowing SC12Orch Installation procedure to install Web Server:
This is the current Web Server (Installed) Role Options before starting the SC12Orch Installation procedure:
Question: If IIS is not installed before the installation of Orchestrator does Orchestrator install it correctly?
Question: If IIS is already installed before the installation of Orchestrator does Orchestrator validate that the correct IIS features are installed?
Answer: No. The prerequisite checker for Orchestrator appears to only check that IIS is installed, not validate that the correct IIS features are installed which Orchestrator requires.
Thank you to Paul Johnson both for tracking this down as well as for working with me to format this into a FAQ approach to answer these questions!