Just spoke to the organisers. Even though it IS legal to be on the harbor on a SUP with no PFD, it looks like PFD's will be compulsory in all major events.
As a surfer it does not sit well to have wear such a thing, but after speaking at length to a number of people in and around SUP and ski racing, I am starting to see that if we want professional, well run events, we are going to have to get used to it.
Here are the arguments that have been out forward as to why PFD's will be mandatory for most racing events-

To grow the sport, organisers have to cater to everyone who wants to participate

To include everyone, safety has to be of the highest concern.

One incident could put a spotlight on our sport which could lead to even tighter regulations on recreational paddling requirements.

As most distance racing is longer than 40 mins you need hydration. If you need to carry hydration it is not a big step up to get it in your PFD. Most good PDf's come with a bladder option.

If you want to eventually race down-wind or off-shore you are going to need a PFD.

According to even the most hardened opponants of PFD's who have Ski raced for many years, they all say they are no more constricting than a Camelback and do not take long to get used to.
Sounds like we have to get used to this in all major events if we want to participate

For those that want to compete this Sunday and don't have a paddling specific PFD, the organisers are making available a Type2 rated PFD with hydration on the day.
PM for details if you want to pick it up on the day.