Personally, I don't see this as cheating. In fact, if it is, I'm guilty of it many times. As far as I've ever known, shooting through walls (penetration-wise, not clipping) was never considered cheating.
I'll tell ya, I've gone as far as to go into a local server and test every single wall and window in Donner, Ava, etc. to see which ones bullets penetrate. I see nothing wrong with maximizing success using non-exploitive game mechanics. There has been bullet penetration in dod for a long time. There are a whole bunch of places that the MG42 can shoot through in Donner.
Again, I've never heard of this considered cheating as it's a well known dod game mechanic. Furthermore, how can you reliably enforce it. For example, if someone is in a window and you start spraying the window, there is a strong chance that the bullets that kill the player may have actually gone through the wall, not the window opening. Is that cheating?
--Mr. Bildo