Does the Forest Service operate an emergency radio frequency? And if so, what channel on a hand held walker could I find it?

No, the Superior NF does not have an emergency radio frequency.
However NOAA , National Weather Service does, follow the link to their frequencies.

Link

Just wondering are you talking about using an emergency radio to call for help if something happens?

My understanding is Northern Tier. Has a radio tower and will forward a call if they receive it. Not sure what channel or how it is monitored. Also not sure that it works for The Whole BWCA but It would work for a large swath around Moose lake since it’s a pretty tall tower. Northern Tier crews that go BWCA Do so with radios they can call in with in case of emergency, when crews go into the Quetico they take a SAT phone.

From an emergency standpoint for calling for help in case of an emergency I would NOT personally take a radio. I would bring an InReach, Spot or I think another one might exist.

This year on a family trip I took an Inreach device.

Ryan

A PLB, Satellite messenger, or Satellite phone is the only thing you can rely on for emergency use. A two-way VHF radio could be useful for either conveying additional information when possible or for not-quite-emergency situations. I'm not sure what Northern Tier has - it's probably a closed commercial frequency I would guess. If you get an Amateur Radio Operator license, a good chunk of the BWCA is covered by 2-meter ham repeaters, but that does require a license for each individual who would be using them, and again that's not something you can count on for an emergency, just a supplemental option.