It’s possible, but it might not look good. Sometimes, it will look fine. Other times, it will require adjustment. What happens when the source model strokes her hair, but the destination model has longer arms? For a FK-driven source, her arms will probably pass through her head.
I’m currently working on an IK heavy rig controlled by few bones. What I would do, if I wanted to transfer animations from another dissimilar rig, is adjust the source skeleton to be the same size of my model and use “copy position” constraints (possibly copy other stuff too, depending on how the destination rig works) on my IK control bones, pointing to their sister bones on the source rig.