October critical patch update

First, excuse the dumb questions - I'm not a DBA, but a software developer tasked with supporting a product that runs on an Oracle platform. We endorse one version of our application to run in 2 environments. Those environments are Oracle 11.1.0.7 with APEX 3.1 and Oracle 11.2.0.3 with APEX 4.1.

My question(s) are as follows:

1) Will this patch work in these environments?

2) Will it even install?

3) Is it really required/needed?

4) Is the critical patch update really tied to a specific version of APEX? If so, what should I look for if using a different version?

Thanks for reading this far and for any responses you may have.