It looks to me like there's more convergence than divergence in both of the shrouds. Also, the article states that they're trying to create a low pressure area behind the blades:
"FloDesign wraps its wind-turbine blades with a shroud which operate on the principle that separating the air into two streams (one going through the blades and one going around them) creates a vortex at the tail-end of the turbine when the two streams converge back into one. It is that vortex that then adds extra 'pull' on the turbine blades, causing them to spin more and/or at greater efficiency."
When you think about it that's really what you want. A jet engine has lower pressure in front of the blades. Spinning them pulls air in and compresses it, creating a higher pressure on the back sides of the blades that then goes into the combustion chamber. Now reverse it for your wind turbine. You have high pressure on the front of the blades from the wind's impact and they are curved so that lower pressure on the back will create a turning torque on the turbine.
The outer shroud appears to work like a reverse augmentor tube, creating a low pressure area at the back of the small shroud to increase airflow through it.
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