When first time the device uses or saves an VPN configuration, the device shows a prompt asking the user for permission to install it, but just for the first time. If you have other VPN installed in the device you can see in the settings app which one is active in that moment with a tick on it.
Once installed the VPN profile, you do not have to do more, when you open your app, the device uses the VPN profile associated to your app automatically, but if there are more VPN profiles associated to other apps, then each app will use its profile.
If the question is: Can you use only your profile for other VPN apps? The answer is no, sorry.