Do Cerberus and Ahalgana need to be defeated for the “defeat all rival units” win condition to be achieved (for Bloodshed, Spars, and winning via defeat in other Sport events)?
No. The best units are arena units, not rival units. As such, they do not need to be defeated for the “defeat all rival units” win condition to be achieved.
Note that on Pluto’s Refugees Side B, there is an arena rule that the beasts need to be defeated for non-Sport even wins, but this rule is not present on Side A.