it depends what kind of "webcam channel" the OP is talking about. Being able to view a local-network attached camera, like a baby cam, etc., that could be done if the cam broadcasted using hls. If he's talking about a Skype-like channel, the Roku just is too limited in its abilities to handle that.
I was just fixing to post a question about this. We were thinking about hooking the computer with a webcam to the tv for Christmas, and I was thinking it would be cool if the Roku had a channel for this.