Well if the package states Epic compatible then the animations will work with any Epic based skeleton. This also includes the Paragon characters which uses the same Epic based rigging and in context is usually referred to as a framework asset as it’s practical use is the same across all similar assets.
That said when imported into a project a typical animation package will contain three required components. The animation as data, The base skeletal rigging usually the Epic rig, and the mesh detail that also contains the necessary weight data.
How all that data can be used depends on the context of the piratical application so lets say we set up a project using the 3rd person template.
For ease of understanding lets say that the original is labelled “Epic Skeleton” and as is out of the box you can run around using the 3rd person base animations.
Now lets say you want to add a 3rd party animations when you import the package into your 3rd part project you will have a copy of the “Epic Skeleton” that is referenced by the animations contained with in the purchased animation package.
To use the animation “data” contained with in the purchased packed you do not need to retarget the animations but rather change the animations reference to the “Epic Skeleton” of the original project and you can then make use of the purchased animations as part of the 3rd person template.
Another option since the purchased animations are generally contained with in it’s own folder you could just delete the referenced Epic Skeleton and Unreal 4 will tell you that it is referenced and give you some options such as changing the reference path to the 3rd person template version.