Is it just as effective to mix fat in at the end of a curry?
Fat helps carry flavor, it also add to the mouth-feel of the final product.  Fat also adds flavor.  So, getting the "flavor into the fat", or probably better put, to be carried by the fat, is only part of the equation. So, in part this depends on why the fat is necessary for a particular dish.  There are all types of curries, so clarifying your recipe and purpose would be helpful in, at least partly, answering this question.  As @Cindy points out in the comments, since you are adding this at the end, it would be easy to reserve some of your product without the extra fat added, and compare it with the final product once the fat is added.  See which you like better.