ABAP is ABAP, no matter which module or which application you talk about. The reason why you see IS-U ABAP or MM ABAP, or APO ABAP etc is that they expect you to know that particular application well enough to quickly figure out the tables, transactions, BAPIs, User exits etc available in that area. IS-U has no specific need for special ABAP skills except in the print workbench area which too is not unique to IS-U. You just have to be aware of the various modules in IS-U, the business transactions/processes and basic understanding of how they interact with the CRM module, with the web etc. IS-U is the industry specific solution for utilities. So if you look for its documentation, you will get that basic understanding. If you are seasoned ABAP person, you will be able to pick it up really easy.
