I read this thread http://ru.esotericsoftware.com/forum/Unity-Asset-Store-16686 and there's said about 2 options:
Which option suits me?1) They can license Spine, which grants rights to build any number of applications using the Spine Runtimes. In that case, see Section 2 of the Spine Editor license:
Spine Editor License Agreement: s2
2) Otherwise they can include the Spine Runtimes license with their applications, which means each of the users of those applications needs a Spine license.