"Since your average Android application does not have sufficient permission to access /dev/* entries on your system, you must use a proxy called the mediaserver in order to communicate with HW codecs."

This is incorrect. Application access to hardware de/encoders isn't a matter of permissions. You can't get at them directly because the api isn't in the SDK/NDK. However, if you're willing to pull in headers from AOSP, and fool around with dlopen/dlsym you can develop and build against libstagefright.