Is it permissible to say "Ya Ali (AS) Madad"?
Islamic salaam is that the first person says "salaam-un-alaikum" or "as-salaam-o-alaikum". And the other says "wa-alaikum-us-salaam", and it is better to add "wa rehmat-Ullah" after it.
As far as saying of "Ya Ali (AS) Madad" and "Peer Maula Ali (AS) Madad" is concerned, it is the religious rite of the Aga Khani Ismaili’s who pronounce these sentences when they meet each other, and nothing more. And Allah Knows the Best!