Yes, you can load a CSV spreadsheet into Yellowfin. A CSV spreadsheet can be loaded to drive a Yellowfin report, or to load data into a table that can be joined to other real database tables in the Yellowfin View.
You might be asking, “Why not Excel?” There are too many inconsistencies to cater towards in Excel e.g different datatypes can be loaded into the same column, filters, merges, etc.