Not true. I've been using the app since day one on my 6th gen touch. The app itself doesn't react well with any device with the "GPS not found" message; I've seen it on my sister's iPad mini, my iPod touch, and my friend's iPhone 6. However, I learned that if you open Control Center or Notification Center with the app still open then close it (it doesn't even need to be fully pulled up/down) it resets the GPS data (however still sometimes a little inaccurate) and the app continues to track your location.
Using it while tethered, connected via Bluetooth, makes the app work slightly better, however it still is a bit inaccurate when you aren't near wifi networks to ping off of to tell the app where you are more accurately.
Happy Pokémon-ing!