Yes, a Samsung SmartThings Hub is required for operation. Spruce uses the Zigbee wireless protocol, and uses the SmartThings Hub as a bridge.
Spruce is compatible with both Smarthings Hub v1 and v2, which was released in September 2015. More information on SmartThings is available at the SmartThings Homepage.
The interface for Spruce is in the SmartThings App, available for iOS, Android, and Windows Phone. It is not possible to use Spruce via a PC or web browser.
While Spruce will probably connect to other Zigbee-enabled smart home hubs, Spruce has been optimized for SmartThings, and functionality in home automation hubs will be limited, and is untested.