Yair,
[quote user="Yair Raz1"]1. Has anyone used these devices/drivers in the context of TI-RTOS?[/quote]
TI-RTOS 1.21.00.09 as a Graphics Lib Demo example for a TM4C123GH6PGE.
[quote user="Yair Raz1"]2. Besides the drivers, does GRLib support the concept of an OS? Do I need to implement a special GUI task that will monitor the widget message queue and respond to events?[/quote]
I don't think that this example uses Widgets, so I can't say for certain on what problems you might be running into. From looking at the grlib source code, the widget module's message queue and mutex primitives are not implemented to use an RTOS's equivalent APIs so you don't have to implement anything extra.
I hope this helps.