So after further testing, answering cellular phone calls from your iPad does not require Bluetooth, but Handoff of apps does require Bluetooth. Having Airplay on is not needed.
BTW, If you answer a call on your iPad, you can then go to your iPhone and tap Return to Call and it will finish the call back on your iPhone.
I can't wait for Yosemite and for SMS texting from your iPad and Mac. That's going to be really nice.