pretty hard question to answer, i guess given the exact right conditions the chances would be close to 100%. i like the idea of having more than one male in any colony or even reverse trios. the boss male then can exhert his dominance and show the girlies how tough he is.
some people have bred a pair I believe, but many seem to have better luck with a colony of 5 or more, in a bigger tank. ( have 5 adults and some young in a 4 ft tank for example)
what size is your tank and what tank mates were you planning?
I have quite a few zebs tanks, my breeding tanks, are all 7 fish, 3m - 4f. Tried a while back to split into pairs or at least 2f-1m, but didn't work, seem quite settled in a group of 7 in a 3ft tank.