i gess there can be some danger, snorkles can mess up the air flow to the motor and can make a bike run too lean or too rich wich can be bad on a bike if not fixed, this is a common thing that happens but can be fixed by rejeting or even adjusting the air/fuel mixture screw. if the snorkel is not sealed up good around the air box it can let water,mud,and/or dust in the air box and may make its way into the motor,this should not happen as long as you make sure you seal up everything good. for the exhaust snorkel, 4wheelers can be totally differnt, some bikes will run all day in water but some exhausts will shut off when whater goes over it, you will just have to find out for yourself by putting your hand over the exhaust to see how easy it shut off or the more risky and some times more accurate way by accually taking the 4wheeler in the water just to see if it shuts off. i always would just take mine in the water to see if it would shut off but eather way will work.
-Aaron