Can a person with an abdominal aortic aneurysm lift weights safely?

No. Lifting weights will increase blood pressure and that may cause problems with the aneurysm.
Depends. If the AAA is below the threshold for repair (~5cm in men and ~4.5cm in women), then lifting weights is relatively safe. Once the aneurysm reaches the threshold for repair, it is safest to refrain from lifting heavy weights until the aneurysm is fixed. More importantly, regular surveillance with an ultrasound / ct angiogram as well as good blood pressure control is good medical management.
Avoid heavy lifting. Heavy lifting or straining leads to increased blood pressure - this can put pressure on the inside of the aaa.