Nigel,
I can't say from direct experience of your particular servo, but my ProCat is running an older 2000 series KO servo with the blue 'hot-wire' lead, which is connected directly to the + battery terminal on my ESC. This servo is probably mid-90s era so long before the invention of the LiPo battery, but has been working faultlessly in my LiPo equipped buggy
From memory a pack of old-style Nimhs could peak at 9v - of course this would drop as soon at the charge is stopped but I'm sure your servo would be ok being powered by an 8.4v LiPo ;-)