It happens but is extremely infrequent. Mostly if congestion is present. I've only known of one person in 30 years that absolutely couldn't clear their ears and dive. My regular buddy to this day has problems occasionally - by mid-week he's fine though. I suffer from pollen allergies but surprisingly we do a lot of Spring trips and I've never had a problem.
If you think you might have a problem, ask them to demonstrate the various ear clearing techniques, there's about 4-5 common ones. And go real slow and try one or more of them repeatedly if you feel any pain/discomfort - even as often as every foot or continuously - stopping as needed. Sometimes it helps to rise a little then continue down also - my buddy does that frequently.
Popping an eardrum in your area could be very bad - when the cold water hits your eardrum you'll likely get vertigo or severe disorientation.
If you do feel a little pain, it will likely ease at depth - which in your case will be above 40'. If you feel more pain, don't push it.
There are also OTC medications that help - mostly pseudephedrine (sp) based. I have a friend who starts on a maintenance dose a few days before our trips so he's usually fine on it. I'm pretty sure he takes Zyrtec.