Hi Mohit,
What do you mean HR Data getting replicated to ECC? Do you mean all the Employee Info?
HR Trigger works when a change in some Infotypes/SubTypes(mentioned in Decision Table) is observed - which inturn refers to the change in PA Tables. So as far as there is some change in PA Tables in ECC, Your HR Trigger should work.
For Example, If you have mentioned in Decision Table, For any change in Infotype 0105(Communication) and Subtype 0001(SY-UNAME), trigger HR HIRING. Whenever this Infotype/Subtype changes, a change is seen in PA0105 Table.
I haven't tried it personally, But would be interested in knowing your results 
Regards,
Fazil