Can I connect any Thunderbolt 1/2 device to a Thunderbolt 3 adapter?
Yes, you can use the Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter to connect your Thunderbolt 2/1 devices to your new MacBook Pro.

From Apple's webpage:


  The Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter lets you connect
  Thunderbolt and Thunderbolt 2 devices — such as external hard drives
  and Thunderbolt docks — to any of the Thunderbolt 3 (USB-C) ports on
  your MacBook Pro.