If its a straight line relationship as you describe the summary fields can do it. You can do something like role up into BOL Assignments something like 'Driver Assigned' - then summarize that field into BOL by the same name and then roll it into Drivers to make your status. Your summary field can be the 'Has any records' boolean value and just keep in your grandparent / great grandparent you're just summarizing where that child summary field is checked.
Functionally you won't have any issue - you may just want to make the fields in BOL / BOL Assignments non searchable / reportable since that value doesn't make sense in that data context.
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Chayce Duncan
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