will steps continue to be counted when in airplane mode on Apple Watch?

Yep! All basic functions of the Watch that don't require a connection to other devices will work perfectly. Basic functions that will work when in Airplane mode include, but are not limited to: step tracker, heart rate monitor, stand goals, etc.

Hope this helps,
Richard

I believe so. I often put my watch on in the morning and forget to unlock it. Late usually! Lol. When I do eventually remember, it has counted all my steps/exercise/stand ring while it was on my wrist and locked.