Yes it's possible in tableau.Have all sensitive data at database and write wrapper calculated fields in tableau.
For ex: take substring of ssn id and display last 4 digits
Alternatively you can implement row level security in tableau or at database level
hope it helps.
The best method of supressing data that you intend to be able to download through Tableau is to do your supressions before loading the data into Tableau.
Another method that might work for you is if you click the Edit link at the top left side of the screen on the data load menu, you might be able to aggregate your data to the correct level, as well as hiding all unused fields (i.e. your original unsupressed field). I can't guarantee either will work, you will need to test them.
Although this is not exactly what I was looking for, but your first solution has provided me a proper way to think about the solution that I was looking for.
Thanks Peter, will check.