This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
You can install multiple JDKs in Tomcat and assign them to projects on a per-project basis.
However, as William has pointed out, Java has an excellent mechanism for providing legacy support for older versions of Java from newer JDKs. That's a feature that has been part of Java since the beginning, and one of the reasons why I pretty much abandoned less civilized development platforms.
Customer surveys are for companies who didn't pay proper attention to begin with.