When it comes to putting flowers on your cake, there are many options available to you. Fresh, silk, fondant, gum-paste.. all are good ideas the only real worry is to make sure anything you use is food safe for the cake. As your baker, I have to assume all parts of your cake may be eaten. (A bride I knew used gold fish in her center pieces and after a few drinks and a dare, many of the gold fish were eaten!)  Use what works best for you for colors,textures and financially. As long as they match the rest of the wedding flowers, you can’t go wrong!