Danny,
We have discussed this topic before and the jury is still out. EBC makes pads for our bikes with different materials, standard, Kevlar, and sintered. Our discussion in the past has been whether the sintered pads would cause accelerated wear on the rotors, as sintered pads contain powdered metal for greater wear/longer life. Several members are using them, but none have mentioned any rotor wear yet. A standard, or even a Kevlar set of pads should not void your warranty, but the sintered pads could generate more wear and heat than the rotor is designed for. Like I said, nobody using them has reported any problem, but it could be an issue. If your dealer tells you he won't back you up if you use something aftermarket, you're pretty much up a stump...
As to not reusing worn pads when a rotor has been replaced due to warpage, well, that makes sense. The pads are probably worn uneven and on a fresh rotor surface that could cause problems all over again.
