Also remember that WETM and WHAM are both owned by ClearChannel. Even if there was some coverage overlap, it's not like he's working for a competitor.
It's been a few years since it last happened, but sometimes when WSYR (then WIXT) was in a pinch, they would borrow meteorologists from sister stations in Binghamton or Utica.
Conversely, when a smaller market is in a bind, you may see a Syracuse or Rochester meteorologist on the air (though usually, taped at their own "home" studio as opposed to actually appearing in person). It doesn't happen often, but it's nothing new.