Good morning Chandu,
An easy way to tell whether ARKit is used in the background is to check how fast the CanStartTracking function returns true after creating the instant tracker. For ARKit is should take a while before you can make the switch from initialization phase to tracking phase; for our internal algorithms it should happen much quicker.
Having said that, I'm not aware of any issues with the internal switch to ARKit as of now in the 8.0 release.
- Daniel
chandu burle