I got the V2 hub from US/Amazon. I realize now that EU use different frequencies 
Can I use this hub for the upcoming EU expansion or do I need to get a EU hardware hub? Thanks.
Legally if your in Europe you need the euro version as the us frequencies can cause problems with European devices in the 900mhz spectrum. From a technical point of view as long as you only use zigbee devices, It will work.
Also Amazon has an excellent return policy.
Ignoring the legal aspects of slightly different Z-wave frequencies in EU and the US (same frequency for Zigbee devices), you can also use US devices with your US hub.
Fairly easy for battery operated devices, more complicated for AC powered devices (you need a step-down 220v->110v adapter, and plug adapters).