If you would like to use the Spine Runtimes to play the outsourced animations in your game, then yes, you need a Spine license to distribute the Spine Runtimes. Note you can distribute any number of games or apps containing the Spine Runtimes with a single Spine license. Spine Essential is sufficient to use the Spine runtimes in your apps (unless you make more than $500,000 USD in one year, then you need Spine Enterprise).

If the outsourced animation is exported as images or video, then you don't need the Spine Runtimes and therefore don't need a Spine license at all.

If you would like to edit the animations in Spine, you would also need a Spine license. If the animations use Spine Professional features, then you'd need Spine Professional (or Spine Enterprise).

Hello,
I have a similar question.

I am developing a game in Unity for a client. He outsourced character animations to another freelancer who has a Spine Professional license.
I understand that one of us also needs a license in order to distribute the game. The client will be distributing the game. Is it enough if only I buy the license or does the client need one too?

If the client is distributing the game, only the client needs a Spine license. If they make less than $500,000 in gross annual revenue, Spine Essential is sufficient for distributing the Spine Runtimes, otherwise they'll need Spine Enterprise.

The reasons for you to have a Spine licenses would be:
1) you want to use the Spine editor for editing Spine projects (note you can use the Spine trial if you just want to view the Spine project files), and/or
2) you want to distribute applications containing the Spine runtimes.