It'll work. But most wideband instructions tell you to put it within a certain distance of the collector to get the best reading. I imagine there's a time difference to think about between the collector and rear O2 bung. That being said, I've done it with no noticeable issues.
My Holley Terminator instructions say the sensor should be between 1 and 10 inches after the header collector AND you must have no less than 18 to 24 inches of exhaust pipe after the sensor.
Not saying in the H pipe won't work, just letting you know what the experts say.