Philip Spence has admitted three counts of grievous bodily harm. The plea was entered last week but could not be reported until today because of a judge's order.
He is due to go on trial this week for attempted murder, which he denies.
One woman was left in critical condition and all three suffered head and facial injuries.
The April attack, and a later attack on an Emirati family in London, were front-page news in the Gulf nation, where violent crime is rare.