Is the following statement about workflows and sub-workflows (subprocesses) true?

The statement isfalse. In SailPoint IdentityIQ, there is no strict limitation on nesting sub-workflows (subprocesses) up to 3 levels. You can nest sub-workflows as deeply as required by your business logic and system design. However, it is advisable to manage the complexity of nested workflows to ensure maintainability and performance, but there is no enforced limit of 3 levels for nesting.

References:

SailPoint IdentityIQ Workflow Guide

SailPoint IdentityIQ Administration Guide (Sections on Workflow Design Best Practices)