I think you can use the OEM tweeters, but you might not be pleased with the results if running them with the aftermarket component woofers.
The 60.9cs component system comes with a nice crossover. This ensures higher frequencies go to the tweets and all low-mids go to the woofer. In the OEM setup, I believe the 6.75" door speakers are "full range" (e.g. get the entire frequency of the signal), while the OEM tweeters have an inline resistor which moderates the frequency and prevents frequencies below a certain point from reaching the tiny speaker.
If you do get this component system and opt to stick with the OEM tweet, using the Kappa woofer with the crossover might not sound great because the Kappa's crossover shift point frequency and the OEM tweeter resistor-determined frequency might not match up too well. You might be missing out on a certain frequency range of the sound signal. Conversely, if you instead skip the Kappa crossover and run the full signal to the Kappa woofer while keeping the OEM tweeters, I really don't know how it'd sound, as they're not designed to handle higher frequencies.
In either case above, you're not really running the speakers as they were designed to operate. I recommend following Infinity's guidelines. But if you're curious as to how it'd sound in another configuration, it doesn't hurt to try! Then you can wire up some other configs and compare them to find which appeals best to your ears. Feel free to give it a shot and let us know how it sounds!
Oh, one more thing.... if you want to keep the OEM tweets, I believe you can look into picking up a "full range" Kappa 6.75" speaker rather than a component system. My thought is that the "non-component" Kappa woofer might handle a full range signal more accurately.