Mixamo license

no you are fine... hacking a Unity or Unreal game to get the assets is pretty easy but that is because they are old software aimed at students now which isn't something you as a designer have any real control over

in other words thay hacked your game = on them not you

the licence allows you to use Mixamo assets [models, textures or animation] to make a project and doesn't really limit you very much as long as your project follows the rule of one

if a person can download your project and remove the asset [model, texture or animation] from it then you have licencing issues i.e, if someone wants animations etc they need to Mixamo and get it from the site, not from you