In the UltraGanttView, is it possible to have gaps in a task's bar (effectively splitting it into multiple side by side bars)?
The expected usage is for a task handled by a single resource that is assigned elsewhere for a period of time to display a gap for the time the resource is not active on the task.
What you describe here sounds like task splitting, which MS Project supports but UltraGanttView does not.
If your objective is to make the task's UIElement display as two pieces, you could probably use the IUIElementCreationFilter interface, but the effect would be strictly visual, and to be honest it might require a considerable amount of onerous coding to get it working.