I seriously hope they are sealed and wont cure to what corten usually does which just looks like pure rust like this bridge in Glasgow, Scotland which is 'cured' corten steel:Yes, you can apply sealants to Corten to mitigate staining and further corrosion.
There’s still potential for failures in the seal but, I suspect they’ve been monitoring the grates over this past year. They’ve been installed behind the walls for a while now.