WhatsApp calls with background data disabled
Yes, you will receive the calls on WhatsApp normally, even with the background data turned off as long as you are connected to the Internet (via Wi-Fi in your case).

WhatsApp makes use of a framework called VoIPKit available in iPhone software development kit, which enables it to receive audio/video calls even when in background/not running status or with the device in sleep mode/locked state/screen turned off.