To get around this issue, I've had to use the DateTime type, but this is not ideal in all circumstances, especially on report filters.
Thanks for sending in the question. I just tested this using a MS SQL Server stored procedure and my date fields are being interpreted as dates in the Yellowfin view.
I tested this on the most recent official release (20160701). Could you verify which JDBC driver you are using to connect to your data source?
The reason I ask is because I did a test here, and I can confirm that if you are using the JTDS SourceForge driver that ships with Yellowfin, the date column is interpreted as a VARCHAR instead of a date. This doesn't occur when using Microsoft's own JDBC driver.
In the most recent release of Yellowfin we actually have started shipping with Microsoft's JDBC driver so the switch is pretty easy to make if you upgarde. Alternative to this, you can always download Microsoft's driver and test this yourself without upgrading following the steps in the below forum post:
How to Add New Drivers for Use in Yellowfin
Anyway, I hope this information has been helpful. Please let us know if you need any clarification etc!