Hi Megavlad!
You can import frame by frame animations, although as you may know, the main aim of Spine is to allow users to reduce the amount of frames needed.
You can import the various frames by adding them under the same slot.
Since you're mentioning an animation system, you might be interested in skins, and how, by placing each frame under its own skin placeholder, you can actually speed up importing new frames in Spine with the new skin duplication settings. (info can be found here Skins - Spine User Guide: New skin placeholder )
There are unofficial user-made scripts to import the frames and key them in an animation, (I made one too explained here: Quick method of creating animation from frame images )
It's also planned to add better frame by frame support in the future, as you can see here: Frame-by-frame animation support · #9 · EsotericSoftware/spine-editor
But we have no ETA for it.
I hope this clarifies things a bit, otherwise feel free to ask! 🙂