I was able to install the latest (1.4.2) using JDK 7 with no issues.
The other thing I did was modify /etc/ambari-server/conf/ambari.properties
I commented the section pertaining to java. I can’t recall the exact section since I’m not around the server at the moment, however it was pretty obvious. I remember this causing me problems if I didn’t do it, Ambari would try to install JDK 1.6 if I didn’t modify the properties file.