If your tortoise gets lots of sun, then I don't think you NEED the D3. But I don't think it hurts anything either. The amount in most products is relatively low.
In order to KNOW the answer to this, you would need to carefully determine your tortoise's calcium needs and vitamin D needs- there is a chart at http://tortoiselibrary.com/nutguide.html that will help you determine this. THEN you need to figure out what it is actually getting in the diet and lighting.
Ok Thanks for everyones help! While Im at work they are inside but when I come home I put them outside. I use the powersun bulbs while inside. My lil guy has been sluggish so I was just wondering