Not necessarily. They don't cover everyone - most spreadbetters are just punters and don't need to be covered as they end up losing anyway. Any new spreadbetters, unless I guess placing especially large bets, would be assumed to be punters and wouldn't be covered until they started to look like serious investors. Also, in stocks with equal amounts of longs and shorts, they would cancel each other out and the company would just pocket the spread.
That said, I expect the company will probably only take so many bets on any one company just in case the price goes haywire.
It's only the winners who absolutely have to be covered, and I would wager that that's an embarrassingly small number of accounts (not that anyone will admit it on here!)