TL;DR - No.
I’m posting this here so that no one else spends hours going down the rabbit hole to try to figure out if it’s possible to use this service. Bunny Optimizer is a service that can (for some sites) convert all images (including ones uploaded to the CMS) into webp format. Unfortunately, it doesn’t work with Webflow sites as the images have to have the same domain name in file URL as the site. Because all Webflow images are hosted on the global-uploads.webflow.com repository, they are viewed by the Bunny Optimizer as external and are not copied and converted.