I'm not sure, but I think the only "rule" about extraneous "stuff" in photos is if you're uploading a photo to the entry for a specific plant in the database. In that case, fingers and toes and furry friends are discouraged.
But my feeling, at least, for multi-plant images isn't so much to post a pretty picture (although most are!), but to show different plants growing together in different geographic areas and how they complement one another. My humble opinion only, tho.