I have NRaas_ErrorTrap and NRaas_ErrorTrap_Tuning_DisableDereferencing in my game. Do I need both or only the tuning?

You only need the base ErrorTrap, not the tuning. The tuning mod wouldn't work without the base mod anyway, and each tuning mod has a particular use, so if you don't need to adjust ET itself, you don't need the extras.

The tuning mod that disables dereferencing is specifically for fixing long loading times due to a feature of the base ET. From the documentation: "Only use this tuning file if you are encountering an unacceptable slowdown during load-up." Even then, it only addresses one cause of long loading times, so if you added it and found it didn't help, you'd want to remove it and look elsewhere.

In other words, you or rather most players want Dereferencing. The tuning file deactivates an important part of what ErrorTrap is designed to do.