Wouldn't limiting Germany's ability to become powerful enough to be a major threat have been in the Allies' best interest? How was Germany able to get to a point where they were a threat to most of the European continent, despite the Treaty of Versailles?
In the beginning it was largely done in secret and was fairly informal and were small things that flew under the radar. It became more formalized and rigorous as time went on, the the covert nature became harder to hide. The effort was exposed around 1930. After It was exposed, Germany already had regained power and economic vitality, and rearmament became much easier after Hitler withdrew from the League of Nations in 1933 when he took power. There is some discussion, and legitimate discussion, that the rearmament was basically and largely a "look the other way" problem from the get go. There were various reasons for this idea, and most of them derive from economic theory and power balancing among nations (in this case, Russia was fast becoming powerful, a leaning towards diplomacy rather than aggression and war in the aftermath of WWI).