The Process Data Mart and BAM database store the same information. The information in the Process Data Mart is more consolidated and it stores it for longer periods of time.
You can use the data in the Process Data Mart to contextualize BAM data.
The Process Data Mart database and BAM database share the same schema definition. The only difference is that the tables in the BAM database start with the "BAM_" suffix. This allows use to easily re-use the SQL queries you define for BAM.