Hmm. I thought I replied to this thread, but that seems to have gone missing.
Long story short, you'll have to gt lucky to even have snow in those parts at that time of year (or any time of year in recent years).
If there is snow, the only place worth going in northern Germany is Braunlage (Wurmberg), and even that is pushing the limits of what you would consider "worth it". There are a couple of runs, none of them challenging, and if they're claiming 1000 ft vert that's a bit inflated. It is also insanely crowded on holidays and weekends. I'm talking hour long waits for the gondola crowded.
Braunlage the town I find interesting. It has a distinct feel of faded glory. I got a lot of visitors back in the days before cheap flights, but now most people overlook it. I like, some people probably don't.
If you are looking to go for a day or two midweek from Hamburg, why not? Even mediocre skiing is still fun. If you're going for a week, I'd look at getting a cheap flight to the alps.
One big caveat: if you like cross-country skiing, it is very good in the Harz mountains (not just Braunlage). Again, assuming there's any snow.