Thanks!

Additionally, we can use other datasets if it is available to everyone, like very popular open-dataset??

I'm not a zindi staff so this is my two cents of wisdom. please take it with a grain of salt.

They specifically allowed pretrained models and open packages but not datasets. meaning that you can't bring an external dataset as it may result in license issues later on when deploying the winning model.

point being, use anything as long as it is meant to be used publicly and freely by anybody.