Neither of those will work out of the box. You'll need to do some work if you want a decent DragonBones runtime for MonoGame.
The DragonBonesSharp repo is specifically for unity. And IMO the code is really messy. I think it might even be easier to write a runtime from scratch than to port theirs to use it with MonoGame.
EDIT: I just had another look at the repo and they improved it a lot since I last looked at it. The core seems to be completely seperate from the Unity stuff, so that makes it seem like it's way easier to port to MonoGame than I initially though.
The other repo is a runtime I wrote last year. It produces a lot of garbage and it's out of date (the export format changed a bit in DragonBones). It does not support inverse kinematics or the new bone weighting feature. I you don't want to use those features or are up for implementing thrm yourself, my repo is probably a better starting point. I don't intend to work on the runtime myself in the near future, but if you have any questions or need some help just pm me here on the forum or on Gitter.