Sure. There is no direct way to tell if the other app is installed, unless you add a mechanism for that. You can directly access anything you want in the other app, as long as you implement a method to do that. None of this is difficult.
I can't make any statement about whether app review will allow any specific app or feature. I'm not app review. You have to submit and hope. However, these kinds of operations are commonly done. As far as I understand the guidelines, there is no prohibition on it. If anything, it would be encouraged. This is usually only a problem when someone tries to do these kinds of operations with Apple apps, usually as a way to circumvent the sandbox. If you are integrating with your own apps, you should have no concerns.
Just make sure that your app works fine even if the user hasn't installed the other app. And also make sure that you aren't obviously violating some other guideline. You haven't said what your apps are doing. If one app is a keyboard extension, for example, then it would be forbidden from launching another app. If one of your apps is some kind of catalog of apps, then that could violate other criteria. But if this is just two regular apps, then they should work together.