Sure, you can patent it, if it's something that hasn't been done. Kevin Beller got patent 5148733 for the Duncan Trembucker poles. There's been others too, like Fender's patent (2968204) for dual magnets under the strings, or between the strings (as on a P or J pickup), the adjustable poles on the G&L pickup (4686881), and there was another one by a guy who's name I forget, where he had poles that were basically steel tubes, so it was a round pole piece with a hole in the middle.
The DiMarzio thing is a trademark, and you can see it doesn't apply to double cream Cavin pickups with 22 poles, or Lawrence blade pickups. But that's not covering the poles, just the look (trade dress) of the pickup.
Does Nordstrand have a trademark or patent on that pickup?