Where is the documentary evidence for the presence of PKK fighters in Armenia? We have videos and pictures of Syrians fighting on the Azeri side already and plenty of media from the Azeri and Armenian side in general so why have we not seen any PKK fighters recording themselves fighting the Azeris?
I don't know the nuances of the Syrian mercenaries in Azerbaijan but its always better domestically and militarily to have a few more foreign hired guns killed instead of your own troops. Less anger internally and one less soldier to replace with a retrained and reequipped man. AZ has kept mum on their casualties but Putin has said 2000 soldiers on both sides have died so far and almost 5000 total:
https://tass.ru/politika/9792147. That is a large amount of casualties and not easy to replace. For context AZ has 67 thousand active and 300 thousand reserve personnel (if the 2000 figure is accurate that would mean 3.08% of Azeri active personell have become casualties). Armenians would be hit even worse having a smaller active army and reserves.