though the uni probaly wouldnt want to admit it, but students do get into the course with a uai below the published cutoff. though i would not want to bet on it that it is guaranteed. it is always better that you get a uai above the cutoff so that you know you will get in, than get a uai below and hope for the best
if you see the program to which you initially intended to get into have a lower published uai cutoff in the main round, do not reject your main round offer. often, the cutoff is higher in the late and final round (sometimes a lot more higher).