Just a note about Apple documents; It's important to reccognize that what Apple doesn't say is just as important as what it does say. For instance, in that article it simiply states "To administer OS X Server on Mountain Lion, use Server app version 2 or later on OS X Mountain Lion."
Not only does that statement say what you use to administer, it also says what you can't use. (Any other version of any other management software.)
This seems counter-intuitive to anyone who has used RAC or LOM on other Intel hardware because they understand that RAC/LOM is a firmware or hardware feature and really has very little to do with the OS. Dell, for instance, has a completely seperate PCI card that serves this function with its own network interface, power supply, etc. These methods of remote access simply don't care about the host OS or whether or not the host even has an OS.
This seems to be the case with Apple Xserves, though the NIC is shared, of course; there is apparently a third-party tool that will get to the LOM features of the Xserve, though I've never used it myself. (See above) So the defficiency in this case appears to be the management software itself. The "Server Monitor" app isn't compatible in some way with Mountain Lion and they didn't integrate that functionality into the "Server" app so it's broken.
Though if that were the case, you would be able to use Server Monitor on a Snow Leopard machine to access the LOM on an Xserve running Mountain Lion Server but you can't. So the Host OS must be doing something hinky there. (I vaguely remember an issue with NIC binding in Lion... I think it had something to do with LCAP?)
Anyway, it's just not working right now... I upgraded some workstations to Lion but haven't pulled the trigger on Mountain Lion yet and I won't be upgrading the servers past Snow Leopard Server any time soon... In fact I need to track down a few serial numbers before they're all gone!
