System update over the air on WiFi fails through Proxy.

I have a proxy setup in my wifi settings. My question is, will a proxy prevent the System update over the air (wifi) from checking to see if there are any updates available?

In my enterprise environment I have all port 80 traffic being pushed through a web filter/proxy. After allowing port 5353 (which is what I am seeing the system update check traffic being on...namely 224.0.0.251:5353 whenever the request is made) and all traffic to and from the said IP. AND allowing all traffic to and from 208.44.23.58 (which is where the software update XML file is being pulled from: http://mesu.apple.com/assets/com_apple_MobileAsset_SoftwareUpdate/com_apple_Mobi leAsset_SoftwareUpdate.xml) to no avail. The only way was to let all traffic to pass from our internal network out and vice versa - which is unacceptable.

I am also contacting Juniper networks technical support as seeing this could be an issue with our SSG-520.

Any info on this would be helpful.