From the docs in Blender.org:
I can’t really tell if a voronoi shader would work or not in GPU, because I don’t use GPUs for rendering. But by the documentation, as long you don’t use Cell or Simplex noise functions, you’re safe.
(the voronoi example posted above uses the cellnoise, so you would need to replace that with some other pseudo-random function, for it to work in GPU)
Starting to reconsider my choices in life
Hahaha, only fools never change their minds ! It’s the first step toward improvement 
Procedural textures are always interesting learning opportunities, but when it’s more about using your skills or doing paid work, the questions are : Am I going to get faster to the result ? or Is it going to look better than using bitmap textures ? and most of the time (with blender) the answer is no to both…
However, while procedural stuff are longer to make, in some situation that can lead to better result, but I highly doubt it with this particular case.
What I tend to do most of the time is to grab several textures from internet and mix them in a procedural way.
Then it’s possible to have many advantages of procedural materials : high details, non-repeating patterns, some customization/parametrization…
And some advantages of photo based textures : believably, fast to make, complex patterns.
Anyway, for a flower I won’t bother going that road, and having the same texture repeated on each petal probably won’t be noticeable, but if that’s the case you can always pick some kind of a dirt/grunge texture and slap it on top with a very low opacity and you’ll start to break the repeating pattern !
Have fun !