To delineate the drainage basin for a lake, would the pour point be the inlet or the outlet?
I think there are a few things to consider. First, a drainage basin is defined as the area upstream of the point to which all precipitation converges. Flow does not converge at the outlet - flow converges at the lake. Outlets don't contain any additional information of the upstream area draining into the lake. This implies that to find the area draining into a lake, you would necessarily have to proceed beginning from each and every inlet. 

Here's another way to see this. Approximately 20% of all land drains to lakes with no outlets. These are referred to as endorheic lakes or endorheic basins. Even though there is no outlet, there is absolutely still a definable drainage basin area.