I used a dino finding mod ok valguero and a umbra was detected but despawned. The logs did say a umbra spawned, but showed there were 0. This may be a bug, but if your on valguero, you can find Umbras!

According to all of these tips, they spawn on more maps than just Ragnarok

To tame it you need the Drake claw and it requires element shards to shoot.