The Business Intelligence application for Salesforce is a data input tool which is completely unaware of the Records that already exist within a Salesforce Organization so it would be possible for a Salesforce User to create duplicate Account and Lead Records via the application if no "Duplication Rules" are enabled within that Salesforce Organization however should such rules be introduced by your Salesforce System Administrator then the application will abide by them:

Should you happen to have any further queries surrounding Salesforce's management of duplicate records then please refer your Salesforce System Administrator to the following Salesforce Knowledge Article:

Duplicate Rules