Tryout with douardda and I failed so far.
After setting the right logger in the configuration, it actually started logging but only workers event (gunicorn.workers: number of workers managed by the arbiter - gauge).
Tried to dig in in the code but did not find the right solution yet.
There are apparently compatbility issues with the gunicorn workers we use (aiohttp) and gunicorn to send the information we are interested in (gunicorn.requests*).
Well, at least with a default setup 
This still needs further investigation.