Yes, you will need a Spine license to use the Spine Runtimes in your game, even if you do not intend to modify the assets or open them in the Spine software. The Spine Runtimes are required to load and render the animations created by your contractor in Unreal Engine, and using these runtimes necessitates a Spine license.
For your specific use case, where you do not need to edit the animations and only need to incorporate them into your game, a Spine Essential license is sufficient. The Spine Essential license allows you to use the Spine Runtimes in your game without any issues. However, if your game makes more than $500,000 USD in gross annual revenue, you would need to upgrade to a Spine Enterprise license.
Here are some key points from the provided contexts:
In summary, you need a Spine Essential license to use the Spine Runtimes in your game with the assets provided by your contractor. If your game's revenue exceeds $500,000 USD annually, you will need to upgrade to Spine Enterprise.