Is it ok to use splenda if i have renal failure and diabetes?

Depends how much: The premise is that splenda is not absorbable i.e. Will not go to blood to cause systemic effects. However, any substance in large amounts may behave differently and become absorbed partly. Therefore, we actually cannot be very sure that large amounts of splenda is safe. Moderation is the key. Having not seen a surge of kidney failure in the recent years isn't necessarily reassuring.

Splenda and RF: I've looked at sources that i consider reliable and can find nothing that says you should avoid splenda under your circumstances. I would, however, suggest that you discuss this further with your doctor.