Schabe - The original round bridge will work, but will only let you turn the lights on and off. If you want to change scenes, or get access to any future skills, you'll need the second-generation (square) bridge.
@RVidgen - Good catch. One thing to note with the Echo Plus - if you connect a Philips Hue bulb directly to it (without using the Philips Hue app), you can't use all the various scheduling features that come with Philips' app.