Other that the specific issue above, which is pretty much the only known problem, there isn't anything special about Windows Server 2008 DCs that affects any Ghost Solution Suite version, other than the normal issues that affect all AD environments such as incorrect DNS configurations (or problematic DNS arrangements such as
disjointed DNS namespaces) or permissions problems (such as those caused by doing an in-place upgrade of a domain controller, a practice to be avoided), and Ghost Solution Suite 2.5 does everything it does in much the same way that Ghost Solution Suite 1.1 did so there's no obvious reason why your environment would have these problems after the change.
I'll leave the client time out thing for now: it's important to focus on one thing to diagnose it, so I'll stick with the domain question:
Probably the best way to approach this is to walk through a single task start to finish, methodically gathering the logs of what happened as you go so they can be analysed. Since the cause of any problem could be in the GSS server machine, the client machine, the general network configuration, or the domain controller, it's necessary to be methodical to work out which component of the whole system to focus on. The most basic way to do this is this:
1: Select a task to deploy and configure a target machine: you can capture all the important information about that task's specification by using the "Task Scenario" option in the console. That scenario window rolls up the entire task specification in a way that is easy to cut and paste to save.
2: Run the task. Once it is complete, get all the details of the the task log information by opening the task log and using the "Export to file..." menu option to save the details of the task execution.
3: On the client machine that should have joined the domain, there is a logfile maintained by the Windows API which does the final domain join process; normally this logfile is written to "C:\Windows\Debug\NetSetup.LOG" where it contains all the information about the internal operation of the NetJoinDomain API process and the many steps that it goes through during the process of locating, authenticating with, and then synchronising with the domain controller.
With that information in hand, analysing it should help inform us where to look next for information as to the cause.