I certainly hope not, seeing as how I just ate one yesterday. My daddy was quite upset, but I enjoyed it nonetheless.
A quick search online shows no definite answers. Some say it’s bad. Some say not so much. Some say the flower is okay but not the plant. To be safe, keep your dog away from the hibiscus plant. Of course I find the flower quite tasty.
To keep your dog away from these delicious plants, try adding a few drops of peppermint oil, not extract, to a spray bottle and spray around and on the plant. It doesn’t hurt the plant, but dogs seem to hate it. It keeps ants away too.