Heehee, Dawn, I don't think it is an issue with the butter and shortening icing, but the water and all shortening one, yes.
I noted that Jeanne G also uses the same consistency of her icing for both and she does use the all shortening recipe and I have never seen her have a cracking issue.
At one time most folks did use a thinner, more liquid added crumbcoat, but with water evaporation issues, it is just one more precaution.
The apricot jam if heated and used un-diluted with water, will flavour your cake, but diluted and then covered with buttercream, no it really doesn't because you use so little of it and it is really watered down. You are going to be using less than 1/4 cup for even the bigger cakes, if you think that it amounts to very little because there is water added, no it isn't an issue. Sugar syrup or simple syrup will give you a similar affect. But using full strength heated sieved jam, almost hardens, not that you will feel the difference when eating it, but it really does give you a super set edge, so that is basically the difference.
For home use cakes that are going to be eaten the same day and such, I rarely crumbcoat them either, because crumbs are not an issue for me, But if the cake has to sit awhile before being iced, well then I do. I do find that it prolongs the shelf life of cakes and helps with any slightly dried corner issues, of course, it won't work miracles, haha, neither will freezing for this issue.