Separate permission for buttons and workflows

Yes and no. Its adding a relation of the person’s own entity (which they have edit access to) to the entity. This is possible to do without edit access (not sure if a bug or not, but possible)

Calling buttons a “Field” isn’t really true as to what they are though. You don’t have a different button value per entity, which is what you have in a field. I’m pretty sure (but correct me if im wrong) that you can’t query an entity and get the value of the buttons. Hence, while it gets a bit close to field level permissions, I don’t think its exactly what it is.