auto 4wds (236 tcase) can be flat towed, the transfer case can be put into neutral.

3 button (233 tcase) can no be flat towed without disconnecting the driveshaft.

This is all because of the way the transmissions are lubricated and that they don't get proper lubrication when being flat towed so you run the risk of damaging them. For short distances at slow speeds that risk is low, but for longer distances at higher speeds it's not a good idea.

The manual shift 231 tcases can also be put into neutral but there were some risks with that one too, don't remember why.