Using latest 3.3. Documentation says it should be invoked for both dropdown and autocomplete datatable columns. While it does work as expected for dropdown columns, it is not invoked for autocomplete columns. Looking at modules/backend/formwidgets/DataTable.php on line 161:
$table->bindEvent('table.getDropdownOptions', [$this, 'getDataTableOptions']);
Adding a new line:
$table->bindEvent('table.getAutocompleteOptions', [$this, 'getDataTableOptions']);
Solves the issue. It appears that this bug has been around for a long time.
Please let me know if there is a better way of submitting bug reports.