I tested this several times.
The combination of Reckless Aprrentice and Ice Walker should be able to freeze all Targets that get hit by the Hero power. But it doesnt freeze anyone.
I guess this is a bug caused by the lack of casting the hero power yourself.
But from the wording on the Cards it should work without a problem.
Maybe the text has to be changed or the as it now stands Bug has to be fixed.
best regards