The answer according to my limited experience is that it depends on the head.
Some engines will deliver the oil directly from the block to the head via a cast gallery then up into the rockers. This gallery is in the middle of the head right where that little plug you mention is.
If this is the case, the yes you should get oil out of that small plug.
The second method is as described already, by plumbing a line directly to that plug on the side of the head. If the head doesn't have a cast oil gallery coinciding with the block.
Third way that I know is to actually have a copper pipe run inside the engine behind the push rod cover. At the back of the block there is a 1/4 in NPT oil supply that cab be plumbed to the head via a copper pipe.
I have personally seen each of these configurations on different engines that I have played with in the past.
Elias
