For armor stands, setting their tag Marker to true simulates the same affect of NoGravity. However, unlike with most (if not all) entities, the NoGravity tag (for armor stands) seems to simulate the NoAI tag, completely disabling all means of movement.

NoGravity should be expected to only stop the downward velocity from gravity (like in other entities).
Currently the velocity of an armor stand with Marker or NoGravity will still change, it's just ignored.