[ubuntu] Can VMs imported from another PC

Hi all,

Host - Ubuntu 12.04 desktop 64bit
Guest - Ubuntu 12.04 desktop/MSWindows Server 2008
Virtualizer - Oracel VirtualBox

I have following questions;

1)
Can VMs built on an AMD 4-core PC works on an AMD 8-core PC?
I have imported several VMs, Ubuntu 12.04 and Windows Server 2008 from AMD 4-core PC to an AMD 8-core PC. Those VMs are working on the former PC without problem. Re-config has been made on them after import such as networking, uname, etc. It comes to my notice that one/two Ubuntu 12.04 doesn't work properly such as broadcasting on web without sound, screen diming and then returning normal etc.

2)
Do I need to reinstall Guest Addition on a cloned VM?
I have to reinstall Guest Addition on cloned VMs

Please advise. TIA

B.R.
satimis