The V-Play sprite components internally rely on the QML SpriteSequence / Sprite types by Qt. I just tried disabling smooth for the default Qt SpriteSequence, and as you said: This feature doesn’t seem to work for sprites.
There’s not much that we can do about that, maybe someone in the official Qt forums can provide help, or they might fix it for one of the next releases if you report it.
One possible solution you can try is to use the AnimatedImage QML type. It can be used to play GIF animations and the smooth property seems to work with this type. 😉