I guess that your question is related to our previous discussion in this thread. So I will answer this question with that discussion in mind.
Advertising in non connectable mode in the ble_app_uart example is possible but note that it would result in that none centrals would be able to to connect to your peripheral (therefore Non Connectable Mode). In the previous thread you mentioned that you would want to connect to a central first, retrieve some data and then advertise that data in non connectable mode. See this thread.
