4wd needed around Exmouth/Coral Bay area?

Probably for sand dunes around Coral Bay, and crossing Yardie creek depending on what it is like, if open. These of course are off sealed roads, so you need to be certain of your hire contract. The Ningaloo coast is unsealed as are of course four wheel drive tracks like we took across dunes to the coast north of Coral Bay.

If you go around from Exmouth as far as Yardie Creek, past the National Park camp areas - and into them - 4WD not needed. Road sealed, except for short tracks into the camp areas - mostly about 100 metres or so. Then you can go back via Exmouth to Coral Bay - sealed again.
4WD needed only if you want to do the direct route from Yardie Creek to Coral Bay, or as said above, go exploring dunes and back tracks around Coral Bay.

Forget about crossing Yardie Creek unless you have a boat. Cyclone in early 2015 washed all the sand out of the mouth. July this year I witnessed 6m boats coming in the mouth.
Exmouth/Coral Bay a soft roader will be fine.
Ningaloo station access can be very corrugated and a few sandy spots getting into the camp areas. Probably better with 4WD there, or a decent compressor at the very least.