You're trying to write non spatial features to a spatial (polygon) layer.

You'll need to change the Geometry in your writer to "Table"

Thanks for your response hkingsbury. Changing to "Table" creates a fgdb table. How do I create a feature class?

A table is a type of feature class. Are you expecting the data to be spatial? In its current form there is no geometry on the feature to make it spatial

Sorry for the confusion, Yes I'd like the output to be spatial. The dataset I'm joining the CSV to is a polygonal feature class in an oracle enterprise database. I want to join the matching record's attributes of the CSV to an existing buildings dataset and export to a file geodatabase on my local machine.

Is the geometry coming through encoded in an attribute? If it is, you'll need to use a geometryreplacer to turn it spatial.

If its not coming through at all with the databasejoiner, you might need to look at using an oracle reader and join the data with a featuremerger or featurejoiner

This was the issue! The geometry wasn't coming through with databasejoiner. I used an oracle spatial reader and fed both datasets into Featurejoiner and was able to write out a polygonal feature class! Thanks so much hkingsbury I really appreciate the help.