Is it possible to use the GE Link bulb without a wink hub?
There are several emerging standards for home automation, but from looking online it seems like th GE bulbs use Zigbee 1.2. The Wink hub then serves as a bridge between that and your home wifi network.

So if you want to communicate with the bulbs from a Raspberry Pi you will need to get a Zigbee module. If you want the Raspberry Pi to the communicate with other devices (say, your smartphone) you will also need to connect it to your home network via wifi or Ethernet.