Cool whip does not replace properly prepared meringue, imo. I also think there is a difference between condensed milk and a lemon pie filling prepared using cornstarch, lemon juice, lemon zest, sugar, etc....condensed milk is too sweet for this application, imo, and the sweetness and of condensed milk can hide and overpower the tartness of the lemon. Lemon pie filling (and most other cornstarch based fruit pie fillings), should be light, not heavy like a dairy based pie filling can be.
I will have to try this way of making lemon meringue pie sometime soon. I usually make it the old fashion way. I actually prefer key lime pie over lemon meringue.