No. Kiri on Apple Watch should be used with an internet connection. Offline use is not something you should rely on today.
What this means in practice
Voice logging on Apple Watch depends on connected processing, so it will not work reliably without internet access.
Features that depend on live syncing should also be treated as online features, not offline ones.
When your watch is connected, entries and activity can sync back to your iPhone and the rest of your Kiri setup.
Best expectation to set
If you know you will be somewhere with poor signal, it is safest to assume Kiri on Apple Watch may be limited until you are connected again.
Is offline support planned?
We know offline support would be helpful, especially for travel and spotty connections, but there is no offline Apple Watch mode to rely on today.