They probably did but they almost certainly didn't go "No don't put that .jpeg of that character in the game because we might make them DLC. Maybe."
It's probably a lot easier to tailor Spirits than it is to tailor DLC, and with Nintendo handpicking the characters this time around, a large majority of characters that are spirits likely aren't up for the running because they're just not enough of a promotional draw at the moment (Bandanna Dee, Elma, and - unfortunately - Dixie, spring to mind here). Characters that likely wouldn't be a spirit would be characters from titles that are too recent or in development, or third party characters. That's why I think a Three Houses rep and maybe even a Torna rep might be on the cards, but I wouldn't be surprised if DLC, like in Smash 4, leans towards third party, and in this case, you're highly unlikely to see a lot of the characters that would make it in since no one's gonna negotiate a major character like a Dragon Quest rep for a jpeg.
Besides, if you ask me, assuming that a spirit = deconfirm is just way more fun personally speaking because that just means all bets are off on what to expect.