vpn pass thru is it absolutely needed and why exactly

Hi
I've read on the internet that in order to use vpn you would need VPN pass thru. According to my fuzzy understanding it's something to do with it doesn't work with NAT.

the original setup I had was the sky hub natting into the ntegear router's wan port then to rest of the network. I did have DMZ disabled on the sky hub but teamviewer still worked

Teamviewer is not a VPN solution.

Teamviewer requires no port forwarding to work at all. It relies on both machines being able to communicate via a central server

http://www.teamviewer.com/en/res/pdf/TeamViewer9-Man...

See page 22.

Only the case if using the Teamviewer VPN mode, which most people do not for straightforward remote control purposes.

For example wanting to be able to print from a remote PC rather than just view its desktop