I am not familiar with the Smart tail light, but a hub dynamo puts out an AC voltage, and LEDs require a DC voltage. There needs to be some rectification that takes place. In the case of the Edulux headlight, there is a full wave rectifier built into the light - my guess is that the tail light does not have rectification built in, but relies on the fact that the LED by itself will provide rectification. I use the Supernova E3 headlight, which has a DC output from the internal rectifier to power an LED tail light.

What you might try is to go to Radioshack and buy a "Full-Wave Bridge rectifier" It will have two terminals marked with a ~ and then two marked + and -. Connect the two marked ~ to the dynamo, in parallel with the Edelux headlight, and then connect the other two to your tail light - you may need to swap the polarity of the taillight to get it to work right....

Mark