Multiple servers can connect to a LUN provided the server software supports the concept of a shared LUN and it has been configured as such. In most clustering models for example shared LUNs are normal. The max number of servers that can connect is likely a limitation of the server software itself and not the storage controller.
For XenServer pointers I'd look at this blog: http://blogs.netapp.com/virtualization/citrixxen/
Hope that helps.
