I don't why they specify a number of lamps as well as a total wattage. Seems illogical to me. As long as you don't exceed the rated wattage then it should be OK. So if they are (for example) 5W downlights, 11 lamps is 55W which is well within the capacity of the dimmer.
I suppose that if you were to try and run a gazzillion tiny lamps, then there might be issues with masses of capacitance in all the individual drivers, but for a normal setup I don't see that being a problem.