In documentation, SQL Database driver, section : how to build OCI Plugin on Windows. The following sentence is false :

"Choosing the option "Programmer" in the Oracle Client Installer from the Oracle Client Installation CD is sufficient to build the plugin."

In order to build the driver, you also need Oracle Call Interface (OCI) option. So change to :

"Choosing the option "Programmer" and "Call Interface (OCI)" in the Oracle Client Installer from the Oracle Client Installation CD is sufficient to build the plugin."

The test is done with a freshly downloaded Oracle Client for Windows (v.11.1.0.7.0) and the last Qt SQK for windows.

Compiling runs fine. I've not tested the driver itself yet. But I will do in a short future.
This is a modest contrib to a GREAT product.
Regards

Small update : I'm currently working with the QtSql Oracle driver previously compiled (read-only mode) : it works fine.