ARM LCD driver internal workings
Is this safe to CPU to connect just with limiting resistor 


Safe: Yes. I recommend using at least 1kOhm since you probably need multiple LEDs.


  should I use a transistor driver 


That would be rather difficult since you might be unable to use VCC or GND as a potential base. The LCD is driven in AC mode using the LCD_COMx pins, so the voltage on a segment pin has only meaning when compared to the corresponding LCD_COMx voltage.

So you need to put the LED (and its limiting resisitor) between a segment and a LCD_COMx pin. Note that the LEDs light may be barely visible due to the low current and time multiplexing.