Given that 5150 is a police code, like 10-4, or 187, or 211, they could. However, they might have to do it as it's written in the police manual i.e. 51-50, or even 50/150 if they wanted to get creative. It would read phonetically as "fifty one-fifty" or "fifty-one fifty", depending on where you place the emphasis.
DiMarzio sends out C&Ds but they cannot dictate what colors and formats can be used, as colors and formats are not proprietary. I'm sure they'd put up a good argument about the color scheme and format being associated with DiMarzio pickups, but if one were to put a double-cream SuperD and a double-cream JB 10 feet away on a table next to each other, the average person off the street would not be able to tell the difference. If they were informed beforehand that DiMarzio is known for making double-cream 12 pole pickups, then they would invariably say "hey look, a pair of DiMarzio double-cream humbuckers". DiMarzio, however, would argue that a "lesser brand" is being associated with their color scheme, and those who see a double-cream pickup would assume it was a DiMarzio. When it didn't sound like their friend's or hero's DiMarzio, they denounce it as junk and tarnish the name of a company that's respected the world over and they'd go out of business overnight.
It's not protection of brand identity, as DiMarzio would say; it's an outright infringement on the right of free enterprise and a violation of the statutes governing competition in business.