If you make it to the medical, they want to hire you.
There are two medical hurdles to clear. One will be with Etihad as part of the assessment. The next is the GCAA after Etihad forwards them the information. If there is an area of concern at either, in the cases I know of there is an opportunity to clear it up. It is not an automatic rejection.
I had an issue that Etihad wanted cleared up prior to forwarding my application to the GCAA. I saw a doctor at home and resolved the issue. My doctor sent a note to Etihad documenting his treatment and a clean bill of health along with supporting X-ray's. Etihad then forwarded my application to GCAA. That was several months ago and have gotten no feedback from GCAA. I understand that no news from them is good news.
Good luck.