No special requirements set it apart from a bare-metal install. You do need to acquire cluster licenses from your reseller, though, just as you would with a bare-metal install, if you are doing active/active clustering. A single HA pair (active/passive) does not need any additional licensing.
It seems that you have a number of licensing questions --- while there are a few resellers that are on this board on a regular basis (me being one of them, and Bob, and a few others), I recommend that you work with your reseller to determine what your licensing needs are -- if you are not currently working with one, go to http://www.astaro.com/partners/locate-an-astaro-partner -- there you can see who is in your area, etc.
