Well. cities such as Hiroshima and Nagasaki did have military value and they also produced many soldiers and equipment to be used in the war. I don't believe it was immoral to bomb them.
Japan was on its knees mostly because the U.S. had a naval blockade that prevented the Japanese from importing food, oil, etc. The Soviets had nothing to do with that blockade just like the Soviets had nothing to do with defeating the imperial navy and successfully taking islands that brought U.S. bombers to Japan's doorstep. Japanese leadership had no illusions that, somehow, they would be able to hold onto their Asian conquests. So, no, the Soviet entry into the war isn't what compelled Japan to surrender. Additionally, the Soviet conquest of Manchuria and Korea was immaterial to saving Japan from total catastrophe.
Thank GOD the Japanese emperor had enough sense, power and, perhaps, enough will to try and survive. Otherwise, it would have been necessary to burn every inch of Japan to the ground. No doubt, MILLIONS and MILLIONS of Japanese would have starved to death and died of disease, in addition to the millions that would have died fighting the U.S.