That seems somewhat similar to the logic that the US used to decide that Vietnam was strategically important; some sort of minor variation on the domino theory.
Interesting to consider it like that.
The Soviets had no warm water ports on the Pacific, and Vietnam was smack the the middle of key US allies and strategic trade routes for rubber and oil. It was a strategic place.
That said. This isn't an excuse for the insanity of US policy in Vietnam from 1945 onwards.
From my own reading, it seemed that China's involvement was largely due to the Russian, and Chinese push for more "Red States" (which is why they were also involved in Vietnam). There was the notion that Capitalism would fall by the hand of "Global Revolution"...