There are a few things that I can think of to fix this.
Problem: two devices that are (or act as) webservers, both use port 80.
Solution 1: if your router supports port-redirection (e.g. redirecting incoming port 8080 to internal port 80), do that for the webcam.
Solution 2: manually configure port-forwarding to your WHS, and do not forward port 80 to it - it's not really needed, as the WHS main page is actually an SSL (https, port 443) site. All that hitting http:\\<servername> does is redirect to https:\\<servername>
You'd just need to remember that you'll need to need to go to https:\\<servername>, as the built-in redirect won't be there - you forwarded 80 to the webcam.