I'm sorry I don't know enough in the web camera side but as far as I'm aware some streaming methods don't conform completely to HTTP standards. I'm not sure that this is the case here as you say it uses HTTP, but reading the URL a little further would lead me to think the stream is encrypted.
That may also be where web shield falls down as it is expecting unencrypted traffic as it can't scan encrypted traffic and also where I would say it isn't true HTTP traffic as it is encrypted which should really be HTTPS, which the web shield doesn't monitor because it can't decrypt it.
This might be what the web shield is having a problem with as it is expecting http protocol traffic that isn't encrypted.
You have used the Exceptions, which clearly doesn't seem to work, there is another option, Ignored addresses (Web Shield, Customise, Basic, here you can add the IP address not a domain name as you would in the exceptions. This was I believed mentioned by one of the Alwil team in another topic relating to streaming.
Give that a try and see if it works, that is me for the night, almost 3 a.m. here and my bed is calling, good night.