While you can certainly run the EMS w/o the wideband input, having the WB offers some nice options. For instance, you can do automapping when the wideband is setup on the EMS. Instead of creating a fuel table of pulse width, you can do a whole table of desired air/fuel ratios. As you drive around with the "automap" feature enabled, the EMS will re-write the map to hit the desired AFR. It makes putting a fuel map together a LOT simpler!
You'll want to read on how to set it up though. You'll have to cut the wire coming in to the EMS from your original O2 sensor, and connect the WB output to that terminal. Then you'll have to tell the EMS which sensor is going to be your primary, and what WB sensor is connected to it. There's plenty writen about this on the AEM forums though.