Yes, look at the sections on...
Car Wash Mode has some info when the engine is operational.
Automatic Transfer Case has some info about Transfer Case Neutral
Towing a Disabled Vehicle section is of course no help if the engine will not run or 12v cannot be provided.
View attachment 10879
When in Diagnostic Mode (foot off brake, hold push button start for 5+ seconds) and then pressing the 2High button 5 times in less than 10 seconds will show a Neutral Transfer Case Shift begin on the 4x4 indicator on the DIC, but I have not been able to get it to complete and it reverts back in 20 seconds, I have tried rocking the vehicle to release pressure on the gearing but it just won't complete the shift, my guess is, per the manual, that the engine has to be running and the trans in Neutral, I will test that today when I go out, BUT, since the transfer case clearly by the indications on the DIC is initiating the switch to neutral (which as stated above allows the vehicle to roll if the parking brake is off EVEN IF the transmission is in Park) would make a huge difference if GM made the change to software to allow this if the engine wasn't running. Seems easily doable.
Per AXE's post, towing is only supposed to be performed with the transfer case in neutral.