That's the Snakes, not the Foxes.

Moiraine was a bit wrong. Rand asked questions that touched on the Shadow (how to win the LB, how to Cleanse saidin) and wasn't punished. Most likely, it was because these questions were totally relevant to his thread in the pattern. Moiraine and anyone but Rand/Nynaeve would have asked the same thing and probably would have been punished for it. The Snakes read what's already set by the Wheel for your thread in the Pattern, the great events and the "forkings" and can't answer questions not related to you. "Foolish questions" probably implies stuff that is way too trivial to be foreseen in your thread, things that will completely depend on your own decisions/free will. The DO is not part of the pattern either, so you have to be very careful what you ask about it. You can ask how to cleanse saidin from the DO's taint or how to win the LB and live if your TDR (they didn't really answer the how to win part, though... except to tell Rand he must die), but I think you'd get punished for asking about the DO's plans or the plans of those with whom his will, and influence outside the Patern, is involved (his orders to the Forsaken influence their plans, etc.).