Sir, one thing to be aware of when scoping a derringer is the scope's objective bell diameter. If you use a scope with a large objective, be sure it has a steel tube rather than aluminum. You may notice that the top barrel shoots to a noticeably lower POI than the bottom barrel; so long as you know your gun and load, this should not present too many problems.
Also, the objective will interfere with straight ejector rods; be sure to get one of the special right-angle versions.
Hope this helps, and Semper Fi.
Ron H.