If a customer is assigned to a view and the device sending the flows is in the same view, the customer will be able to see flow data.  

This needs to be enabled in the customers' view under the permissions tab.

Go to Configuration, Views, Manage Views and click on the customer's view from the menu. 

Select Netflow stats are visible in this View from the Permissions tab.

The customer will then be able to view flows from the Graphs Browser or the Troubleshooter by selecting the Show Flow Data.

The Flow Explorer cannot be filtered according to a customers view.