RTOS understanding and communication
An RTOS is a kernel that does task management. Despite sharing the name OS, it is very far from OS like windows and Linux, despite what is said in the comments.
Comparing RTOS tasks to Threads is a long stretch.
One has to understand that an RTOS will switch between different tasks when asked to do so. That being said, if a task does not yield, the RTOS may very well be blocked.
There is not much sense in implementing an RTOS for emergency stop management. Because of the task-switching context, and the difficulty to predict the kernel timings and behavior, you much rather handle your emergency algorithm on a high priority interrupt generated by an input or a timer, coupled with a hardware watchdog.