I only play Nod.
Once upon a time, I had to play as filthy GDI and I found it terrifyingly easy to spot stanks. SBH's are also easy to spot if you know where they tend to lurk about.
Still, Whiteout is a tough one. SBH's are too hard to spot on Whiteout, no doubts.
However, if you manage to sneak a stank into the enemy base on Walls without getting noticed, it's all their fault.