It's possible. But, I'm not 100% sure.
Loki almost definitely has a Devil Fruit of his own. He said he wants the last Seastone Shackle off his leg. I doubt he'd care if it wasn't weakening him.
The real question is Ragnir. Ragnir could have a Devil Fruit. The big problem is, the most obvious Devil Fruit it could have is the Lightning Fruit...and Enel already has that. So, it can't be that. It can't even be a Clone-Fruit from Vegapunk, because Vegapunk never figured out how to copy Logias.
So, if it was a Devil Fruit, what could it be? Well...we saw when Ragnir struck the tree it was eventually struck by lightning. So, maybe it's some sort of "Bad Luck" or "Disaster Magnet" Fruit? Something that when you hit the hammer on something, it causes random bad things to happen to what you hit? Either draining the luck out of something, or giving it bad luck?
Or maybe it just IS a Lightening Rod Fruit. And when you hit something you turn it into a lightening rod, too. I doubt that. Because we only saw lightening hit the tree once. If Yggdrasil was a lightening rod now, a LOT more lightening would be constantly hitting the tree.
But, we have seen odd technology in Elbaph, too. Like the Sunstone Painters. And the scene of the lightning hitting Yggdrasil just so happens to look a LOT like "Uranos" firing a bolt of lightning at the Giant Tree from the Chapter 1138 Mural. So, I feel like that's implying a possible connection between Ragnir and "Uranos". Meaning it could be Ancient Technology of some sort. And it's suspected that King Harald was making deals with the World Government without Elbaph knowing it. Maybe Imu gave King Harald this special hammer that works like a miniature "Uranos" as a gift?
The jury's still out. It could go either way in my eyes. I'm leaning slightly more towards it being Ancient Tech, due to the possible connections to Uranos. But, we haven't really seen enough to really make a judgement call.