Downvote is the wrong tool for spam.
Also: spam is so rare in comparison to other downvoted content that in the off chance that the proper tool falls short, of course you can unsilently downvote the spam for the greater good. But as well, when you trigger “report spam” functionality, that is engagement. The server could of course cast a downvote in that circumstance while awaiting moderator action. That would be the most sensible of course.