Do /etc/resolver/ files work in Mountain Lion for DNS resolution?
This question seems a bit old, but I'm going to answer it anyways as I had a similar problem:

Yes, this works.

Your first problem is that you obviously have the wrong IP (8.8.8.8 instead of 203.12.160.35) in /etc/resolver/apple.com. Verify that the contents of this file is really:

nameserver 203.12.160.35


Then scutil --dns should have an entry like this:

resolver #8
  domain   : apple.com
  nameserver[0] : 203.12.160.35


The second problem is that you tried to verify it using nslookup which does not use the DNS resolution mechanisms of OS X. If you look at the man page of nslookup you will find this:

Mac OS X NOTICE
   The nslookup command does not use the host name and address resolution or the DNS 
   query routing mechanisms used by other processes running on Mac OS X.  The results of 
   name or address queries printed by nslookup may differ from those found by other
   processes that use the Mac OS X native name and address resolution mechanisms. The 
   results of DNS queries may also differ from queries that use the Mac OS X DNS routing 
   library.


To check your DNS config you could do

dns-sd -G v4 images.apple.com


and verify if it yields the same IP as 

nslookup images.apple.com 203.12.160.35