I think its pretty much just Ferrothorn (who you'd hit with a Ghost-type move anyways) in doubles, since stuff that carries rocky helmet ocasionally like Cresselia is gonna be hit by the Spirit Shackle. Granted, I'm not that big of a fan of Decidueye in doubles anyways.
I did use Decidueye in special a bit recently, and in battle spot singles, I have to admit that being able to OHKO Celesteela with a Swords Dance boosted Sinister Arrow Raid is pretty impressive! However, Decidueye is actually rather frail considering its low Speed stat (I hate how Mega Tyranitar outspeeds it in particular lol), and it heavily relies on its Z move to function unlike say, Primarina, who has successful variants such as Choice Specs, Focus Sash, and Assault Vest sets. And compared to other offensive Grass-types in Battle Spot Singles, Breloom and to a lesser extent, Tapu Bulu and Kartana, are usually going to be better fits for most teams. I honestly think Decidueye would need a way crazier buff in order to see common use.