The way i see it, Apple does not really have an enterprise operating system for large scale servers. Well OS X Server is more directed to small business with limited users.
There are 2 business here Apple is addressing: Apple Cloud services and OS X Lion. The operating system that supports Apple Cloud services is actually irrelevant. It is well known that Microsoft uses UNIX operating systems for specific services and IBM mostly uses Windows on PC's despite its huge investment on Linux and Open Source.
As long the service is available and online at an affordable price for Apple and OS X Lion is a success, Apple will not move into enterprise operating systems.