I guess it depends on your definition of allies (note the small “a”).
*ally
noun [ C ] us /ˈæl·ɑɪ, əˈlɑɪ/
politics & government a country that has agreed to give help and support to another, esp. during a war, or a person who helps and supports someone else*
*On August 23, 1939, representatives from Nazi Germany and the Soviet Union met and signed the Nazi-Soviet Non-Aggression Pact (also called the German-Soviet Non-Aggression Pact and the Ribbentrop-Molotov Pact), which guaranteed that the two countries would not attack each other.
In return, as part of a secret addendum, the Soviet Union was to be awarded land, including parts of Poland and the Baltic States.
The first pact was an economic agreement, which Ribbentrop and Molotov signed on August 19, 1939.
On August 23, 1939, four days after the economic agreement was signed and a little over a week before the beginning of World War II, Ribbentrop and Molotov signed the Nazi-Soviet Non-Aggression Pact.
In addition to this agreement, Ribbentrop and Molotov added a secret protocol onto the pact – a secret addendum whose existence was denied by the Soviets until 1989.
The secret protocol held an agreement between the Nazis and Soviets that greatly affected Eastern Europe. In exchange for the Soviets agreeing to not join the possible future war, Germany was giving the Soviets the Baltic States (Estonia, Latvia, and Lithuania). Poland was also to be divided between the two, along the Narew, Vistula, and San rivers.*
Hitler and Stalin were allies until Hitler was reasonably sure that his western borders were secure, and he wouldn’t have to fight on two fronts. Hitler and Stalin shared the bad habit of betraying their allies, friends, and neighbors. There is no reason to believe that Stalin would have joined the Allies side without Hitler’s betrayal.