There aren't any currently. See my comment above.

As to your question, we see foreign military planes pretty frequently in our airspace. I assume that they're involved in international training exercises. Typically you only see those when they are entering or leaving US airspace. They turn their transmitters off during training missions just like ours do. Our airspace is filled with US military aircraft every single day that we can't see via these apps because the military planes can turn their transponders off anytime they want. It's pretty cool that we can have this tech, but it's less than perfect for what you and I are interested in.