In the US, flood zone regulations are typically established at the local government level under the National Flood Insurance Program [essentially, they completely bypass state government], so you'll need to check with your local government to determine which if any regulatory requirements apply.
That said, understand that purpose of flood vents is to keep your house from washing away in the event of flood, by reducing hydrostatic pressure against the foundation walls. Anything that blocks or reduces the flow of water, or that potentially becomes debris that can clog the openings will increase the risk of more substantial damage in a flood event.
On one hand, you have to be able to live in your house despite the possibility of flooding, but on the other, there may be an alternative design layout that has substantially little risk of impact. Keep in mind that "built to code" is synonymous with "the worst building legally allowed.