Gidday Clemens,
Diving from Perth to Exmouth, apart from the 'roos, emus, cows, donkeys, camels, police, oversize trucks, road-trains, grey nomads, wicked campers and wedgies, there isn't much to worry about - its a pretty easy trip.
When you camp out overnight - keep clear of trees, it will be prime mating season for the drop bears and yowies - the males need to collect fresh meat for their mating ritual, but if you hang bacon outside they will [usually] take that in preference.
Keep your tent zipped up, and food stowed away off the ground - bungaras have learnt that tourists = tucker, and the ants are known to chew through the sides of eskys for a feed.
The sharks don't read the beach safety signs, so you can probably ignore the signs too / the crocs have scared most of the sharks out to deeper water anyway.
Jellyfish - not to worry, in most places the stingrays have thinned the numbers down, but if you do get stung - either apply liberal amounts of vinegar, or pee on it.
Enjoy yourselves, should be a trip to remember

stephen