To my knowledge, dive shops rarely have anyone who is knowledgeable about medical care at all. What they want, if you are on a prescription medication, is a form from your doctor stating that you are fit to dive while taking it.
I'm assuming you have met the recommended criteria for cardiac fitness for diving, involving a treadmill. You should be aware that there are some cases of immersion pulmonary edema that seem to be associated with hypertension and beta blockers, but the condition is still rare and no one knows what the actual risks are, or whether the medication or the condition it treats is the risk factor.