I think TestComplete reads that list of providers straight from your Windows setup.
I tried a bit of an experiment... if I run the 32-bit version of TestComplete, I get one list of providers, including the OLE DB Provider for Oracle.
If I run the 64-bit version of TestComplete, I get a different list of providers... and the OLE DB for Oracle is not among them.
So, here's my guess... and this may not be the truth of the matter, but only a guess.... If you're running the 64-bit version of TestComplete, it could be that it's filtering out the 32-bit providers from that listing. You might need to download and install a 64-bit version of the Oracle provider in order to use it in the 64-bit version of TestComplete. You might be able to get it from here
http://www.oracle.com/technetwork/database/windows/downloads/index-090165.html
This is documented in the help::
Differences Between TestComplete 64-bit and 32-bit
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To keep your data-driven tests working, use data drivers of the same bitness as TestComplete. For example, if you use ODBC drivers to connect to data sources, then, for TestComplete x64, you must use the 64-bit version of these ODBC drivers. If you read data from Excel sheets or CSV files, you must install the 64-bit version of Microsoft Office 12.0 Access Database Engine OLE DB Provider. Otherwise, you will get an error like “The needed data source driver is not installed or is not configured properly...”. If you have the 64-bit version of Microsoft Office 2010 or later installed on your computer, you might already have this data provider. If not, you will have to download and install it from the Microsoft website. The provider is part of Microsoft Access Database Engine 2010 Redistributable x64: