" Further, there is no mention about whether or not these muni networks utilize muni resources unavailable to private ISPs, such as existing utility truck fleets."
I would be really surprised if the cities don't clearly differentiate the costs in their budgets. Because in today's environment of governments always having fewer dollars than services they are expected to provide, they are going to want things crystal clear if they have to go to the citizens for a tax increase.
As an example, the small city I live in has a public works department that handles streets, sewers, and trash. And they break down every expense, including labor hours, between those services. So for example, we might have 2.4 full time employees (FTEs) for trash service. And you can bet when they work overtime helping to plow streets that OT is billed to Streets.
And we have funding for each of those services. Each one has it's own budget that must be balanced. As a result, I don't see any municipality incorrectly reporting costs to make muni-broadband more attractive. Not when they'd be passing those costs to services that citizens hold in much higher regard as essential. (Police, Fire, streets) They don't even combine expenses between water and sewer, and we get those on the same bill.