Yes, RaiderIO now supports linking all regions associated with a single Battle.Net account together into one RaiderIO account.
To do this:
- Visit the Blizzard Account page on RaiderIO: https://raider.io/settings/battlenet
- If your Blizzard Account is currently synced, click the red "Disconnect Blizzard Account" button at the bottom of the page
- Look for the list of multiple regions and click however many you have characters on that you want to claim
- Click "Link Blizzard Account"
And that's it! A few seconds later you should see all of your qualifying characters showing up in your characters list.