Updated: 05/14/2008 ( See original post below)
It won't work! (adding the command-line backup-tools when CTP(2) is installed) At the end of the process I checked the $host variable (thanks Marco) and it showed that v1 is the current version. I jumped into conclusions too early and got fooled by PowerShell console title :(
Installing the backup-tools via serverManagerCmd (like the MMC) installs ALL backup dependencies (PowerShell v1 and all backup-features), it removes CTP without any confirmation. However, PowerShell CTP2 still appears under Control Panel > 'Programs and features' and the CTP2 program shortcuts are still available in the Programs menu but it points to v1 (installed by serverManager).
The confusion stems from the console title which shows: 'Windows PowerShell V2 (CTP2)' as it appears in the shortcut. I should have check the $host output or make sure that the CTP text logo appears in the console, CTP versions logo says:
Windows PowerShell V2 (Community Technology Preview - Features Subject to Change)
Copyright (C) 2007 Microsoft Corporation. All rights reserved.
So, my apologies for misleading you! I'm still researching the issue and hope to find a solution (if possible).
There was a discussion at the PowerShell newsgroup regarding the inability to add the Backup-Tools feature when PowerShell CTP is installed on Server 2008. I was already installing Server 2008 on VM, so I decided to give it a try. I had no problems whatsoever and the installation was successfull. Here is a video capture of the process. The capture includes the following steps:
Server 2008 is already installed (default install)
1. Install PowerShell CTP2 on Server 2008.
2. Adding the Backup-Tools server component (registers the Windows.ServerBackup PowerShell snap-in)
3. Reboot the Server.
4. Loading the ServerBackup snap-in and listing its cmdlets.