Yes, but it's generally unwise. All the sports you listed are in the Summer Olympics. Someone competing in two sports at the Summer Olympics first has to qualify in both sports. There's no guarantee the fencing and ate know do trials won't conflict. Then, assuming both national sports federations approve, the athlete must follow the schedules of the sports. All the sports you list are tournament sports, meaning winners advance to subsequent rounds on later dates.
So the potential of a conflict grows as the athlete advances. Also remember that event venues may not be near one another, so getting from one venue to another quickly in a large city might be impossible. Lastly, there's less time for the athlete to prepare and recover from each competition, meaning s/he is at a disadvantage in both sports.
In short, it's tough way to go. The dual sport athlete doesn't necessarily face the impossible, but even under the best of situations it's tough enough where it's not a good idea.
