DB2 achieves scalability and performance optimization through techniques like partitioning data across multiple nodes, enabling parallel processing which distributes the workload and enhances performance. 

Organizations may opt for alternative IDEs over IBM Data Studio for managing DB2 databases in scenarios where specific database features are required that are not supported by IBM Data Studio. Additionally, factors such as preference for open-source solutions, cost considerations, and the need for extensive customization capabilities may lead organizations to explore other IDE options. For instance, if an organization requires advanced analytics capabilities or integrated machine learning tools, they may choose alternative IDEs that better fulfill these requirements. Similarly, organizations with strict regulatory compliance requirements may prefer vendor-specific solutions that offer specialized features tailored to compliance needs. 

Performance tuning in DB2 encompasses optimizing various aspects of the database system to enhance its efficiency and responsiveness. This involves leveraging optimization features within DB2 to fine-tune database configurations, query execution plans, and resource allocations for optimal performance. By effectively utilizing optimization features, DB2 administrators can improve query response times, reduce resource utilization, and enhance overall system throughput, ensuring optimal performance in demanding database environments. 

RTO stands for Recovery Time Objective in the context of disaster recovery. It represents the targeted duration within which a system or service must be restored after a disruption or failure. Achieving a low RTO is essential for minimizing downtime and ensuring business continuity during disaster recovery scenarios. 

The buffer pool in DB2's architecture plays a crucial role in caching data and managing data in memory. It stores frequently accessed data pages in memory, reducing the need for disk I/O operations. This improves performance by speeding up data retrieval and manipulation operations. 

To determine if an index is being used by the query optimizer in DB2, you can analyze the explain plan of the query. The explain plan shows the execution steps chosen by the optimizer, including whether indexes are utilized. 

DEFERRABLE constraint in DB2 postpones the constraint checking until the next COMMIT or ROLLBACK operation, allowing flexibility in handling constraints within a transaction. This feature is particularly useful in scenarios where you need to temporarily violate constraints during the transaction and enforce them only at the end. 

Performing regular audits and compliance checks helps in identifying deviations from established standards and ensures adherence to regulatory requirements. It allows the administrator to take corrective actions, such as updating security policies or access controls, to mitigate risks and maintain compliance. 

Buffer Pool is often optimized during performance tuning in DB2. It's a memory area where data pages are read from and written to disk, and optimizing its size and configuration can significantly impact performance. 

The UPDATE command in SQL is used to modify existing records in a table. It allows users to change the values of one or more columns in one or more rows in a table based on specified conditions. It's commonly used to update data when there are changes or corrections needed in the database.