Since the bypass operation on the legs are usually not involving the intestine so there is no reason not to feed them on the next day. As the name of the operation is not given so I am unable to say if the Aortic surgery was done.
How ever the aspiration pneumonia after surgery is possible with any sort of operation as it involves the lack of/suppression of the cough reflex due to sedation or the after effect of anaesthetic and is more to do with the monitoring of the sensorium of the patient to check if the patient is ready to feed. It is unrelated to the surgery type specifically.