How large could this niche be ? Is Zeus a significant factor ?
We already discussed these SPECwebssl figures pretty much to death back when Opteron was released.
In the real world I think people use Apache and MS software, because it's easier and most web servers aren't limited by the server (most are limited by bandwidth or by the fact that they are so boring noone ever looks at them).
Their load balancer software may be more used - it doesn't show up in surveys like netcraft.com