You can for older devices (so your app has to target only those I think) but with added permissions that you will definitely question It seems it is more complex or impossible now: https://developer.android.com/training/articles/user-data-ids#mac-addresses
It does. But it also means that if you want to reset the tracking you would need (for every app) to also clear the storage of the app and logging off and log back in with a different account before starting to use the app again