Do they matter to cops? If they get paid, they get paid by tax money, no?

As I mentioned in another comment, apparently the PD splits the ticket revenue with the school district after the camera company gets their installation and profit margin covered. Cops get paid their salaries from the PD budget which is mostly from tax revenues but also from other sources like tickets and these cameras. A higher PD budget means more perks including higher salaries and paid overtime and more benefits, so while they can't just stuff the money in their pockets (usually) they do benefit from these alternative revenue sources.

does that make you a roving part of the survailance system, too?

Probably. There's nothing I can do about this without losing my job.