Why not? Go a little easy with it until you learn about it's strength when going directly to the flower beds. I have never seen and do not expect to see a test report on tortoise poop. Set yourself up with a couple of test spots that are similar and let the plants tell you...possibly more or less would be better. Put a tablespoon full in a quart of water. Let it set a week and try it on some house plants. Into your compost think likewise. In a pile 4 X 4 X 4 that is relatively new try a five gallon bucket full. Half that much if the pile is half finished. This is not rocket science but you can overload a pile or garden with any manure or other fertilizer.
Good question. Good luck. Not to many folks have or know where to get tortoise poop. LOL