Does summary judgment dismissing an action against a party also mean that it's a dismissal "on the merits" and/or "with prejudice" (both conditions, o

That depends on the basis for the summary judgment.  If, for example, summary judgment was granted because the Court lacked jurisdiction over the defendant, that would not be "on the merits" (which also means the dismissal is without prejudice.")  If summary judgment was granted because, for example, the undisputed facts showed that the defendant had not breached the contract on which he/she was sued, that dismissal would be "on the merits" and "with prejudice."