As far as I know it's still solutionsam.com for 7.5. Do you have both HTTP and HTTPS open? I opened up the PL XML file but it doesn't apepar to have the DL URLs so I'm not certain. Regardless, you probably want to open symantec.com and microsoft.com as well since SIM may send you there for KB articles or to download pre-req software / components.
If you plan on using patch management, the NS also needs to go to various third party websites to download patches and updates. The actual list of sites may vary depending which patches you enble from which vendors and the list could change over time. For this reason, Symantec created a tool which can generate a custom list for your NS. See the below KB for more info and to download the tool. It will generate a txt file with a list of URLs you can whitelist in your proxy or firewall.
http://www.symantec.com/business/support/index?page=content&id=TECH186657