Does that airport have a military base located there?
The 233.7 would be the military comm frequency and you won't be able to pick that up on your scanner. The 118.6 is the civil frequency and as long as your scanner will support the air band, you'll be able to listen on that frequency. They'll probably use the civil frequency for the airshow, but that is just my guess.
But yes military and civil frequencies are separate.
If it is for an airshow, they'll have designated frequencies for use at the show. For example, at the California Capitol Airshow here at KMHR, they've had a defined set of frequencies that they use (for the past three years, it's been the Blue Angels or Thunderbirds VHF frequencies), so those should be able to be heard on a VHF scanner. When the show is over, they'll go back to the normal VHF frequencies.
What I suggest, is to check to see who is scheduled to be there, and cross that with what is listed at FreqOfNature. If it is one of those there, they'll have the frequencies that you can add to your scanner.