How to let a modded mob spawn in overworld, not just Nether?

I've been working with the RealmRPG: Demons mod and wanted to make mob spawners in the overworld that spawned enemies from this mod. However, for some reason, the spawners only work in the Nether dimension. I tested blaze spawners in the overworld and they work fine, so I am a bit lost. Is there some action I can perform in a datapack to let these new mobs be spawned in overworld spawners? Thank you in advance.