Yes, staff discourages (but does not forbid) posting spectrograms.
Standardized to what?
This is only true if the “anyone” involved happens to be familiar with the same scale. For example, I look at hundreds of audio files a day for work and can easily recognize my focal species in a spectrogram because I always use the same scale. But if you handed me a spectrogram on a different scale, unless it was very close to the one I use, I likely wouldn’t be able to identify my focal species.
I think there is a common misconception about what is involved in reading a spectrogram.
Because of this, no one can universally recognize a known species from just any spectrogram. The scale eBird uses is probably the one some people are most familiar with, but there is just too much variability. I’m not even sure if Merlin and eBird use the exact same scale even though they are both Cornell applications.
There is a feature request (Automatically add a spectrogram view to observations with sounds ) that if executed, would produce standardized spectrograms for iNat when audio is uploaded. But there are many logistic hurtles, so it probably won’t be implemented soon.