Uploading saves from the Dreamcast?

Is it possible to upload saves directly from the DC from Planetweb Browser 1.0?

No, but the original Dreamcast web browser (Dreamkey) allowed the downloading of saves from the official SEGA server.

Any other browser that allows DC uploads here?

For the browser question, I don't know. But you can use Dream Explorer, it allows you to upload saves on the VMU.