Constipation as such with an ileostomy that worked would NOT be possible. The small intestine does not remove water from the stool as does the colon. As your colon would not be in use, the poop could not get hard and thus not cause constipation.
What CAN happen is that a person can get adhesions around the small intestine which would cause a blockage from the outside of the small intestine thus squeezing it off. Also you CAN get a food blockage if you eat too much roughage and do not drink enough water so that food gets stuck in the stoma and cannot make it out.
Also you CAN get a small intestine twist where it is brought out through the skin to make the stoma.
So all sorts of things CAN happen. But constipation as we know it is impossible. In fact if I eat too much sugar or fake sugar or grape juice or any liquor I have diarrhea. Soooo, no worries about constipation as we know it in the usual sense.
hope this helps. Rosemary