What are the current restrictions on iOS emoji usage?

I am making an app which contains emojis as follows:

1. Categories such as "Business", "Technology" etc. exist and near them I plan to show a suggestive emoji retrieved from the server.
2. In the navigation bar, when chatting with somebody, there is one of three emojis shown next to his/her name depending on the text messages received.
3. I have a view which I display when there is no content to show in table views. It contains a suggestive emoji.

As far as I know, there were a lot of apps rejected in February because of emoji usage and I can't really find any strict guidelines about how to use them in my app. Do my use cases break the rules?

Thanks.