There are a number of different VPN protocols and configurations, some more permissive than others. In general, if you can ping a device on a remote network segment that is connected via a VPN, then you should be able to see that device in your IP Scanner results, but we have also seen exceptions so your mileage may vary.
1) you may need to add the remote network segment that you wish to scan to your scanned segments (from the Tools menu: manage network segments -> add custom range)
2) you may need to make the scan results more permissive by enabling these three prefs:
• show hidden devices
• include non-local devices
• show devices on ‘virtual network interfaces’