The 100 pF cap is looking into an ohmic impedance of between 200 and 300 ohms over your frequency range of interest (see Fig 9). So at 30 MHz that means that the 100pF cap is forming an input high pass corner of (1/(2.pi.300.100pf) = 5.3 MHz. So the 100 pF cap should be fine for operation down to 30 MHz.
You do however need to put a cap on CFLT1 (pin 3) to get the 30 MHz signal into the part (there is a discussion and an equation for this in the Basic Connections section). Also you need to put caps on FLT2 and FLT3 (pins 16 and 1) to low pass filter the output signal so that the carrier gets removed. If you don't do this you output will be a full-wave rectified signal with the carrier sitting on it. Values and equations for FLT2 and FLT3 are also discussed in the Basic Connections section.