I've never had any issues with zoa/zoa compatibility.
Some other people thought they had though.
I believe in the natural looking tank and to me it's ok to see SOME competition for space.
I would define competition mainly, in this case, as how fast they can grow.
I don't believe that we could have a zoa that would really take over for good and be an nuisance in the tank.
When planning a tank you need to see your priorities, space available and to know the fast/slow growers. That will help you a lot.
A good rule of thumb idea would be: Protopalythoas and Palythoas are faster and "more aggressive" than zoanthus spp., generally speaking.
Keep in mind that for every type of zoa there is a different optimal quality of the environment it's in. That could be one of the exceptions to the rule written above.
Most of all, enjoy your tank...
Grandis.