It can kick some people out of ketosis so the offical answer is no. Even if it doesn't kick you out of the pink, it can set off cravings with the colourings, etc. If you can resist, do honey.
You have no idea how pleased I am that the occasional zero coke is allowed I'm one of the lucky ones that doesn't drop out of ketosis easily and it will definitely help on (rare) nights out.
Coke zero is made with malic acid (i believe) which makes it more acceptable than diet coke. Given a choice between diet coke and coke zero, go for the zero!