Cuba was a member of Non-Aligned since the start of the movement (1961). Vietnam joined it in 1976, but at that time USSR has more influence on Vietnam than China. In the late 70s early 80s Sino-Vietnamese war, USSR sided with Vietnam. However, the Non-Aligned movement clearly criticize both USA and USSR for interfering too much with other countries. In the 70s, it seems that China qualify much more than Cuba and Vietnam since China stands mostly neutral (i.e. not liking both) between USA and USSR.
It's just and organization, many south american countries are also part of the movement and had CIA/USA backed dictatorships from the 60's to the 90's. Also, Cuba in the aftermath of the revolution was a non aligned country, it was the course of events in the following years that made it an ally of the USSR.