DU - Uses ML models only …if you go to DU the first step is to select a model…But this can work only on document data and not plain text emails etc
AI center - This is used for non document data as well…like sentimental analysis, text classification or create and upload your own ml model …all of this can be done in AI center
DU is like a part of AI center which is used only for documents specifically where as AI center is used for all kinds of ML models
you have many academy videos which you can go through
cheers