Arnel,
Sure you could still try this but I would not do that until you understand the very detail of changes between Samba 3.0.2 and 3.4 and, on top of this, what is the impact on Zentyal side.
Is migration from 1.0 to 2.0 a real issue for you?
Well, I understand it's not migration but once you have stored somewhere what you need to keep safe, it's pretty easy:
- mail folders
- samba content
- important configuration settings (main IP addresses, DNS, DHCP and FW rules)