But if you want to be sure, check the output power of the VNA, and the maximal acceptable input power of the amplifier. I believe the VNA sends a very weak signal to the amplifier, so that it cannot damage the amplifier. Also, if your VNA plots the log(S11) graph, you should see a more or less constant graph at 0 db. Then in the Smith chart, you'll observe a small spiral around the 50 Ohm central point. You can check the input impedance of the devices by connecting the input to your VNA (S11 cable). That's because they are intentionally matched to the characteristic impedance of the coaxial cables that connect to their SMA connector, which is always 50 Ohm for most microwave devices, except television cables and likes that are 75 Ohm. The input and output impedance of these amplifier is 50 Ohm.
