Can the Exalogic platform be used for non-Oracle applications? E.g. Having an application using Oracle 11g in the data tier and a apache tomcat EE + Java for the middle / front tiers, then potentially get an Exadata for the database and Exalogic for the applications (tomcat).
You can deploy non-Oracle applications or software on an Exalogic machine if you want. Software that is certified by 3rd parties for either Oracle Linux 5 Update 6 64-bit or Solaris 11 Express x86 should run on Exalogic. But note that Oracle does not certify those 3rd party applications.
For the specific case of Tomcat, Oracle doesn't provide support for Apache Tomcat, but as long as a supported JVM is used (i.e. HotSpot for Oracle Linux x64 or Solaris 11 Express) then Tomcat should run fine.
There is a an ISV program called the Exastack Program for partners that wish to optimize their products for Exalogic. Information can be found at http://www.oracle.com/partners/en/opn-program/oracle-exastack/index.html