Vgg sets the Idd. changing Idd changes the performance of the AMP, especially Pout response.
If is best to build up a feedback loop for adjusting Vgg constantly for desired Idd.
HMC980LP4 is a good fit for this feedback loop.
You can also set Vgg to a constant value as you described or even use a resistive divider. But those approaches may cause degradation on performance.
I also suggest to check the on below link, and the links referred on the FAQ.