Not currently. You can post or vote for an existing feature request on Tech Community where they are considered when the Office dev team goes through the planning process.
When creating or viewing an appointment or meeting as the organizer, add-in commands added to the default tab appear on the Meeting, Meeting Occurrence, Meeting Series, or Appointment tabs on pop-out forms. However, if the user selects an item in the calendar but doesn't open the pop-out, the add-in's ribbon group won't be visible in the ribbon.
When viewing a meeting as an attendee, add-in commands added to the default tab appear on the Meeting, Meeting Occurrence, or Meeting Series tabs on pop-out forms. However, if a user selects an item in the calendar but doesn't open the pop-out, the add-in's ribbon group won't be visible in the ribbon.
See Add-in commands for Outlook for more information.