Branding is not considered part of the RTSP feed when webcasting - it will not pass through to 3rd-party webcast (and, in our experience, creates unreliable cloud recording looks as well).
For the time being, if you're really concerned about the look of your show/talk/program, I'd recommend a production suite like OBS/vMix/Wirecast and use a tool like ZoomISO (which is now officially a Zoom product).
For long-term, please submit a formal feature request and let Zoom know that this is important to users! The more feature requests Zoom receives on a specific subject, the more likely they are to implement change.
