In my opinion the sneak attack is a classic move and well within the bounds of the rules. I wouldn't call it gamey or cheating to move your ships over an allies world in order to bypass his mines and then break treaty and attack.
This is not gamey anymore then mining an allies space while under treaty is.
On the other hand, you should expect to reap what you so if you employ these tactics. Don't pull them on someone, and then act all shocked when they don't trust you in the future.
Geoschmo