ePub spec at w3c says
``In the case of fonts, the primary use case for obfuscation''
Fonts are the primary use but the algorithm is not limited to fonts, any resource can be obfuscated (or encrypted) as long as it is listed in the encryption.xml file along with the algorithm so that readers that support de-obfuscation (or decryption) can do so. Encrypted files I believe are suppose to be compressed before encryption, but obfuscated files are not compressed before obfuscation.
mime type is image/svg+xml which correct for SVG, the algorithm does not involve using a different mime type.
encryption file is correct.
A developer of EpubCheck has acknowledged it as a bug on their github.
https://github.com/w3c/epubcheck/issues/1077