If it is closed, you have to apply quite some pressure on the cover before the SD card in the pocket touches the screen. However in theory it is possible.
To remove the sl6000 you open the cover and slide the pda upward. There is no chance the device slips from the case when it is closed. Since the leathet fits quite thight around the device, chances that is slides out of the case while it is open, are small
The producer also makes screen-protectors. Don't know if they make them for the sl6000 as well.