Economic experiments can never really have a control group, so what the Dutch government learns from this will depend greatly on the theory they already have when interpreting the data.
I suppose they should be commended for the effort, but the other issue is that the experimental group is unlikely to represent what things would be like under a truly universal basic income. Incentives throughout the economy will shift and cause reactions none of us can predict, except in very broad strokes. For example, €1000/mo for a tiny experimental group will probably not have the same buying power as the same amount given to millions.