As I've heard, flash is not allowed on any other animal than mankind, so I don't see the need for it on a true wilderness safari.
But, Andy Biggs if anyone should know.

I really only use a flash for bird photography these days, and never on any mammals. Mostly because of practical reasons, as keeping a flash and Better Beamer on my camera setup all day isn't the most enjoyable. Also, it is common to get a green, or 'steel eye', on lions, and is difficult to remove.

I keep a flash unit (on an off-camera bracket) on my combo most of the time, and use fill flash a lot, mainly for catchlights. If a subject needs some fill, it's often too late to try to fit a flash unit as or after your vehicle pulls up. I have a flash extender too but don't often use it...I'm working on making a snap-on fitting for it, so that it can be put on and removed from the flash head very quickly. And I mean <i>very</i> quickly, something that is not possible with the velcro and elastic fasteners it is sold with.

John