Channel 9 is at the discretion of the flight crew. Al Haynes turned it off after reporting engine failure, but before the hydraulic failure became apparent.
In this case, it's pretty irrelevant, since we don't have any passenger reports about the "smoke issue" from the cockpit; from what's been reported so far, the first sign of trouble in the cabin was the cabin PA about in-flight meals for sale going dead in mid-shill.
If the cabin PA went dead, so did the IFEN, and thus, so did channel 9.
So, sure, someone could have heard something, but not much.
The folks at Louis Armstrong demonstrably did a fine job, managing an escalating condition and providing maximum service and coordination (while keeping the field open), and all the signs currently point to a great job by the flight crew as well.
(shuts up)