A personal point of view. Can be wrong. Friends can correct if they disagree.
Saying Ya Ali, Ya Hussain etc is ok, as being Shaheed they are alive... but...
Saying Ya Ali Madad, Ya Hussain Madad etc is not ok. Madad can be called from Allah only.
No doubt, Hazrat Ali RA and Hazrat Imam Hussain RA are greatest of human beings and martyrs. Their super-human contributions are unmatched. Their courage and wisdom are phenomenal that no human pen can describe. No other in history matches their valor and bravery. But both of them also seeked Allah's madad in every situation. The best way to follow Ali and Hussain is to follow Allah, as they did themselves.
Hazrat Ali RA himself said: Shirk is so thin like a black ant climbing a black tree in the pitch black darkness of the night of jungle. We must be careful about possibility of shirk in any manner.
Further: Are we 100% sure about saying Ya Ali Madad. I think there is a margin of doubt (Shak). Prophet Muhammad PBUH said "Jis cheez pe shak ho usey chor do". So its a matter of care that we don't say it. Rather, we can say, Ya Allah, help us like you helped Ali RA. Or Ya Allah, help us like Ali RA used to ask help from you. Or, Ya Allah, help us like you enabled Ali RA to help Prophet PBUH, Islam, and Muslims.