Just to add, in case the developers tweek the boosts:
The breeding den boost is not working in the Arctic when activated in the mainland. The other types of boosts (nest, etc) seem to be transferring their power the Arctic just fine, haven't had any issues with those (so far).
By watching an actual clock, it is obvious the Arctic breeding time is not being reduced- it is still taking the full 4 hours to complete a breeding with the den boost activated. The one hour, heart-shaped boost timer appears at the bottom of the screen but, for some reason, the timer above the Arctic breeding den is not visible during a boosting period.