I'm not sure about your terminology here. "import" a part into an assembly...i'm assuming you are meaning you are assembling a part in to an assembly.
There is no reason for a balloon to not show on a part if it has suppress features. If the balloon was placed and attached to a feature that is later suppressed, the leader will likely disappear leaving an unattached balloon. I can't remember if you have to delete the balloon and re-add it or if you can edit attachment and re-add the balloon.