Frequency is frequency, does not really matter if it is trunked or not. So the antenna will receive them equally well.
Radio Shack has two antenna that tend to be confusing. The 20-283 is their 800MHz antenna and the 20-034 is what they call their 'deluxe' scanner antenna.
I have used the 20-283 and for 800MHz reception, it has been a good antenna. Read through this forum. There are numerous discussion on 800Mhz antennae.