Yes your picture is of the transfer case drain plug. The transfer case fill plug is more to the drivers side. It's a good idea to change the xfer case fluid every 30k. First remove the Fill plug, then the drain plug. Replace the drain plug, and fill with Mercon V. Don't over tighten the plugs in the transfer case, the case is magnesium and cracks easily!
The transmission is technically filled for life, but if you want to service it, the best way is to drop the pan, then refill it thru the dipstick/service port on the passenger side right beside the passenger cat. It can't really be serviced easily any other way because of the internal thermostat that prevents flow to the cooler circuit, so the fluid exchange units at the quick lube places won't work.