Limitation in the number of objects?

When I export a scene containing about 10 objects, even if they all appear in the sio2 archive "object"folder, only a few of them are displayed in by the iPhone simulator.

Is there a maximum of objects you can use with the 3D engine?

Should I always merge all meshes into one single object before exporting?

Verify that the pivot points of all object is centered in order for the culling method to work properly...

No it doesn't seem that was the issue.
But I may have found what is the problem:

When you duplicate an object in blender, for example "Plane", the duplicated object default name is "Plane.001"
I my case, sio2 doesn't render it.
But if I rename "Plane.001" to "Plane2", then it's fine.

It seems that sio2 doesn't like objects names including a dot.
Maybe when objects are parsed by sio2, what's behind a dot is ignored, as if it was a file extension, and so you end up with 2 objects called "Plane"...
Does it make sense?

You should look at tutorial06 - there are a lot of objects and most of them are duplicates (with names of convention such objInstanceName.00x) and sio2 has no problem loading them. I have some myself following this naming convention and they always get rendered...I did make sure pivots were centered as well doing Ctrl-A in blender for visual transform and scale/rotation....

Add this to your loading code:
sio2ResourceBindAllInstances( sio2->_SIO2resource );
This is for 1.3.2 so it may have changed

Please review the video tutorial06 and review the source code...