You can't sneak steady MW's or GW's into data centers in an unmarked truck. And the control systems for the Dutch national grid are not magically spook-proof. Obviously the Dutch know, and their public ignorance is a political calculation.
The only real question is how much is being paid, by whom and to whom, for the Dutch officially playing dumb.
EDIT: Looks like the spooks are redundant. Per Wikipedia:
> TenneT B.V. is the national electricity transmission system operator of the Netherlands, headquartered in Arnhem. Controlled and owned by the Dutch government, it is responsible for overseeing the operation of the 380, 220 kV, 150 and 110kV high-voltage grid throughout the Netherlands and its interconnections with neighbouring countries. In Germany, its subsidiary TenneT TSO GmbH is one of the four transmission system operators.