Can someone have an angiogram if their platelets levels are at 50?

Yes: Yes, if the patient is cleared by a hematology specialist. However if an intervention is planned and then a blood thinner might be used during the intervention and after, a problem could arise. The risks are different - higher - for a patient with platelets of 50 that for a patient in the normal range because there is less of a 'cushion' in case of a complication.

Yes: 50000 is an abnormally low level but is still high enough not to significantly increase bleed risks. But this is the lowest level where most would consider doing an angiogram or other invasive procedures with risks of bleeding.