We have a loop made of these two amplifiers. However, they are on diferent paths isolated with RF swtiches. These switches are not sufficient to grant isolation though. For this reason an oscillation occurs at around 22 GHz. To compensate this, we thought that we could switch the amplifiers on and of. HMC997 on and HMC565 off for transmission and HMC565 on and HMC997 off for reception. Such would occur at around 5 kHz.
Yes you can switch both amplifier on and off. We do not expect any problems with doing that. 5 kHz or faster is also okay.
You may need to reduce the number of supply bypass CAPs. We have used them on our EVBs for cleaning the supply, removing them will not cause any instability. I would still leave the lowest value cap on the board though.