no - there's a difference between having a QX between the brood box and a super full of stores and just between the bees and fondant.
When you have a super above the cluster, the cluster as a whole (Queen included) needs to move up into that box and stay on those stores filled combs to feed - it moves to keep in contact with the food - if there is a queen excluder in the way, the cluster may move up to the stores and the queen gets left behind in the lower box and will chill/starve although the usual thing that happens is that the cluster won't abandon the queen and they will sit there and starve within inches of a whole box of stores: either way, come spring you have a dead colony
With fondant, you just put it directly above the cluster and bees will go up into it and bring the food back to the cluster - you really don't want the queen to get stuck into that.