This is really only true in ERG mode, where the app needs to have the same unit to control and receive power data from.
If you ride in level mode, you can use your bike based power meter as the power reporting device with no problems.
Training Peaks can allow you to set up power zones for custom activities, so you can have different zones for “indoor” and “outdoor” activities.
You may have to choose which activity group each workout belongs to after your TP sync.