Is it safe to delete all revisions of a deleted node?
I hope you are doing your tests on a test server. In that case, yes, they are safe to be emptied, even if it would be better to let Drupal and any third-party module to remove any entity data they have in their tables.

Rather than worrying to empty tables, I would find a quicker way to create a test server that is then destroyed when the test is done.