SURGEdude and me investigated the whitelists a bit more, and vitacl.ww.dl.playstation.net and vitacl.xx.dl.playstation.net seem to be servers the Vita refreshes the whitelists from, as I went through a variety of situations where it occasionally will reset the whitelist with them blocked via URL Filter which didn't reset the lists, unblocking them and doing something that previously prompted a connection error (like clicking the update symbol on a Vita game) did. So there's that, and to note with them blocked it still allowed access to the E-Mail application and even the PS Store!
For example, I was allowed to download Peace Walker again and still having the whitelist stay modified. However, just to note ahead, since we also were looking into copy-restrictions to make blocked PS1/PSP games happen we found out that since the PS3 seems to pull a whitelist from those servers to determine which content is allowed to be copied upon connecting with a Vita, blocking these addresses makes you unable to copy over any content from the PS3.