It's not clear who should register ejari, but usually tenants do it as they are usually more keen to have the protection.
I think it's 240 dhs and wouldn't like to bicker with a landlord for that amount.
Just looked at the website and it says landlord or his agent, in the past we have never had one as we didn't need as we have AUH visas...... Which dont need an Ejari to renew