The Electro 4 cannot split sounds, except it can do upper+lower manual organ, However, it loads custom samples. So you could create a sample that had Hammond on left and brass on right "baked into it." Note that this functionality is very limited... the Nord considers it all one sound even if your ears are telling you otherwise. Therefore you would not be able to, for example, put an effect or EQ on one sound without putting it on both. You also lose all the non-sample based features of the Nord organ, like drawbar adjustability, high trigger point, etc., because the Nord doesn't consider it to be an organ, it's just a sample you loaded that happens to sound like one. ;-)
You mentioned a brass and piano split, that would be done the same way, with the same kinds of limitations. You couldn't use a built-in Nord piano sound or anything with its piano-specific features (like string resonance or multiple velocity level samples), you wouldn't be able to have the sustain pedal work on the piano sound without also sustaining the brass.
So it's doable, but it's a kludge with a lot of limitations. If you can return the E4, maybe another board would be better suited for your needs, like the E5 or E6 or something in the Stage series (or something other than a Nord). Or the E4 can be a nice part of a 2-board rig, using each for its strengths.