Yup. At are a plug alright.
I guess if my 2011 G5 had that plug I would remove it when I was changing oil but from its location I wouldn't expect to see much drain out.
That goes into the crankshaft housing and, as I recall, the little bit of oil that collects in that area gets thrown back into the transmission gears by the crankshaft flywheels.
Beyond that, this area of the crankcase doesn't communicate with the oil reserve.