Am i able to do ab exercises if i have a hiatal hernia?

Of course: Just realize when you increase the pressure in your abdomen, you may increase the hh bulge, so if get a pain consistent with it, take a break (and maybe some tums) and let it pass. Will quickly find if anything specific triggers it to cause discomfort, and can modify workout accordingly. Still need good physical shape / activity, even with diagnosis. Good luck!

Hiatal hernia: Hiatal hernias are internal hernias of the diaphragm within the abdominal cavity and at times extending into the chest. They are not related to the muscles of the abdominal wall. While most patients can do abdominal exercises without adversely affecting there hiatal hernia, some patients do experience increased reflux symptoms either during or after strenuous physical activity.