You can not rely on SOLR 6 (as it is used by Alfresco) for transactional operations. It would technically be possible to verify that a specific transaction has been indexed, but that does not necessarily mean that all indexing work is done for the nodes in that transaction, as work is split into different workers (ACL, metadata and content tracker). It also does not mean that all work done for that transaction has been done without errors. You'd have to separately check each and every node against the index using undocumented, technical check queries.
I find it is generally quite easy to perform such operations without relying on SOLR or a secondary / separate DB. As part of an import, I would flag nodes that need further processing with additional, temporary aspects, and use Alfresco TMQ capabilities to query those nodes in an independent, second stage action / job directly from Alfresco's database., and remove it, when that processing is done. With proper handling of concurrency / locking and batch processing, this typically is sufficient for what I often encounter in those import use cases.