I cannot think of a single thing better for Syrian unity than fighting a war with Israel that was instigated by Israel. It's exactly what Assad needs to consolidate power, because he's currently in the rather inconvenient position of having to rebuild from a civil war he was involved in. If Israel attacks, Assad has a scapegoat for all the societal and economic problems in Syria and allows for more cautious powers (e.g. China) to be more flexible in the aid and investment they provide.