Never had a problem. I have used numerous partner lounges when flying on EY.
Taken from ETIHAD GUEST website:
Whenever you travel in Economy Class with Etihad Airways you can enjoy the luxury of our exclusive Business Class Lounge before your flight at all our destinations, However, when traveling or transiting out of Abu Dhabi International Airport with Etihad Airways, you are invited to use the Al Reem Lounge facility in Terminal 1. For your further convenience, you can also use the new dedicated check – in counter in Terminal 1.