The ToolTip is available for the following elements:

• the calendar events (default value is taken from DataTextField but you can change it using BeforeEventRender)
• the resource headers in DayPilotScheduler (you can change it by setting ToolTip property for each resource)
• the column headers in DayPilotCalendar - for both ViewType="Resources" and ViewType="Days" (you can modify using ToolTip property of the Columns collection items, it's similar to resources in DayPilotScheduler)
  
• the time headers in DayPilotScheduler (you can modify it using BeforeTimeHeaderRender handler)

These standard tooltips are simply transformed into title="" attributes and they should respect RTL text orientation.

It's also possible to replace the event tooltips with DayPilotBubble by assigning BubbleID property. I haven't tested it but I believe you can use <div style='direction:rtl'>your text</div> as your InnerHTML in RenderContent event handler to switch to RTL rendering.