Is it possible to load the JTM via the GTM?

Yes it is technically possible. However, this is not recommended for the following reasons: 

1. Conflicts and Interference: Different tag managers may use conflicting methods for managing tags, data layer variables, and triggers. Loading one TM within another can lead to conflicts and unpredictable behavior, such as tags firing unexpectedly or not firing at all.

2. Performance Overhead: Each tag manager adds its own layer of JavaScript code to the webpage. Loading multiple tag managers can result in increased page load times and decreased performance, as each TM needs to be initialized and executed separately.

3. Data Loss and Inconsistencies: Tag managers often rely on a data layer to capture and pass information between the website and tags. Loading one TM within another may cause issues with data layer management, potentially resulting in data loss or inconsistencies in the data passed to tags.

4. Debugging Complexity: Debugging and troubleshooting become more challenging when multiple tag managers are involved. It can be difficult to determine which TM is responsible for specific issues or conflicts, leading to longer resolution times and increased frustration for developers.

5. Dependency Risks: Relying on one tag manager to load another introduces dependencies between the two systems. If one TM experiences downtime or becomes incompatible with future browser updates, it could disrupt the functioning of the other TM and the tags it manages.

Instead of loading one tag manager within another, it's generally recommended to choose a single tag manager solution that best fits your needs and use case. If migrating from one TM to another, it's advisable to carefully plan and execute the transition to minimize disruptions and ensure a smooth transition for tracking and analytics.