Just because you can hit a backend without a rate limit, doesn't mean you should. In my experience, government IT is very humorless about this sort of thing. Far better to blend in with normal traffic than to stand out as a bad actor.
"Your honor, the defendant took steps to hide their activities, showing that they knew it was wrong"
Especially given how the response time doesn't matter much here! If you're just looking at 2-character license plates, that's 676/5=136 requests to check them all, and you could easily space that out to something like one request per minute to scan the space every two hours.