I feel like adding to this, just to make sure things are covered well:
Yes, all transverse engines use the intercooler as the primary intake track to the engine (boost and vacuum run through it) The Blowoff or bypass valves (still haven't gotten a definitive answer on how they actually function) are plumbed prior to the intercooler. Any hole in the intercooler could potentially draw in unfiltered air and maybe particulates.
The biggest issue I have with this is the comment of boost loss. A 1/16" hole will not leak a significant amount of boost, but what it does do is require the turbos to work harder to maintain a specified pressure. You really won't lose anything (maybe a little bit of turbo response), but the computer will not allow the wastegate control valve (boost control) to open until the pressure is attained. This equals higher shaft speed, which equals more wear. How much more? I don't know, but neither does anyone who has done this mod.
The oil in the intake can come from 2 places: either the valve cover vent that goes right before the forward (Left) turbo or from the turbos themselves. I always have a thin film in my charge pipes and have my forward valve cover vent to atmosphere through a breather. So, that oil comes from the turbos.