The Netherlands were controlled by the Franks, who were nominally Roman allies—but there was a pro-Hunnish faction Attila was supporting in a succession dispute a few years before his death.
Attila’s empire was reported to extend north to the sea, but it’s unclear what that meant—it could have been the Baltic, or Denmark, or the Atlantic coast of Germany.
It's almost impossible to say with any certainty. Not only are sources of the Huns very much lacking, for instance I believe we only know one word of their entire language, but just the nature of his empire makes it very tenuous. Is it possible some rulers in Denmark sent him tribute? Perhaps. Although even the word tribute is questionable there, because what we might consider tribute and what he might claim is tribute for political reasons are vastly different. It's not like attila's Empire was anything approaching what we think of as an established state.
The Huns are the reason Venice was founded as to flee to the marshes to get away from Hun attacks
