I know oracle can be used with DNN with a data provider but I was wondering if doing that causes any problems with comercial modules or the standard modules in dotnetnuke. Does anyone know or have experience using oracle with DNN and the common modules out there?

thanks

Greg - I'm the author of AcuitiDP - oracle dataprovider for DNN.. As Sebastian pointed out, the data provider does offer (out of the box) providers for almost ALL the modules provided by the core. I say almost because I haven't yet converted over the Shopping Cart module to Oracle (primarily because I've not had any users ask for it). 
Generally speaking the oracle versions of the modules (core modules) are the same as the SQL Server version (so for example if forums is at 4.4.3, you would find the 4.4.3 version when you use the oracle data provider too).

I have also converted other commercially available modules to work with Oracle - these include XMod and Content Manager to name a few. I'm always in discussions with commercial module providers about creating oracle dataproviders for them so if there's a specific one that you're looking for, I might have already created a provider. Additionally, some of the module authors have created oracle dataproviders themselves for their modules and offer it by themselves (so that's another option)..
Finally, you can also create the oracle dataprovider for ANY module out there yourself too (assuming you're familiar with Oracle of course). AcuitiDP exposes the same interfaces like the SQL Server version (ie ExecuteReader, ExecuteNonQuery, etc) which allows one to create dataproviders pretty easily - if neccessary.

Please let me know if you have any additional questions and I'll be happy to answer them.
Thanks

Sanjay Mehrotra