The hole is simply a hole in the block. It is into the flexplate/torque converter area and should not be plugged. I've never heard of why it is there, it is on all of the Series 2 3.8L'* that I have seen.
I'll put $20 the gaskets look bad, and another $20 that the gaskets are not the main cause of the problem.
Upper intake manifold is the most common problem on the NA motors. Let'* step back a minute from the LIM gaskets and try to diagnose the problem.
Do you see any external coolant leaks?
Do you note any oil leaking externally and getting on the exhaust manifolds?
If you removed the throttle body do you see coolant in the UIM right around the EGR pipe entrance?
If this is the UIM, the suggestion of changing the LIM gaskets stands. I'd be surprised if the gaskets are your main issue though.
00 Regal GS: All kinds of cool stuff.