Would you also have constipation if you have fecal impaction?

Yes: By definition, constipation is difficulty or inability to have a bowel movement. A fecal impaction preventing movement of fecal matter through the colon would definitely qualify. However, you can still be constipated without a fecal impaction. A fecal impaction requires urgent medical care, as you risk perforating the bowel with the increased pressure and space occupation.