Are you printing in black and white? Then you might see white pixels on the node border if it's in a different color than black, because the printer uses some patterns of pixels to represent the different colors.

If you print in color, the result should be no different than what you see on the screen. The DiagramItem.Draw method is called both when printing and drawing on screen (also in the Overview control and in exported images), and it always draws border lines using the item's Pen value.

I hope that helps,
Stoyan