Ans 1.
Informatica does not support mapplet within a mapplet transformation.
Informatica supports worklet within a worklet.

Please check Q65 and 66:
http://www.dwbiconcepts.com/tutorial/24-interview-questions/35-best-informatica-interview-questions-a-answers-continued.html

Ans 2.
Yes MS SQL Server supports Bulk Loading.
But if we select Treat Source Rows as Data Driven and Target Load Type as Bulk then the session will fail. We have to select Normal Load with Data Driven source records.


Ans 3.
Yes we can use the same session to load same target definition in different databases with the help of the Parameterization; i.e. using different parameter files with different values for the Target Connection object $DBConnection_TGT and Owner/Schema name Table Name Prefix with $Param_Tgt_Tablename.

Please check the article on parameterization:
http://www.dwbiconcepts.com/etl/14-etl-informatica/74-stop-hardcoding-follow-parameterization-technique.html

To run the single workflow with the session, to load two different database target tables consider using Concurrent workflow Instances with different parameter files.

Even you can try for two instance of the same target connected in the same pipeline. Only at the session level you can use different relational connection object created for different DBs.

Thanks !! Answers are great.