I don't see any mention of "Server Admin" for 10.8 in the MAS; just "OS X Server" which is Server.app.
For additional tools take a look at:
They only piece of the old Server Admin that remains for 10.8 (for now???) is Workgroup Manager. There's a link on that article for it.
There are some additional command line tools. Type the following to see what they are: