Yes it’s possible, using one of two different paths. The code for both already exists in the community. 
One, you can just stream to the echo as a Bluetooth speaker. You will need another device to create the files to stream and decide when to stream them.
LANnouncer can do this, among others.
Two, if you set up your own Amazon developers account you can take advantage of a very sophisticated Alexa skill which community members have created which let you both use the echo to make announcements and let you Query the status of devices and a whole bunch of other things. That one is called askAlexa.
You will find both of these and more on the quick browse list for “voice” smart apps in the community – created wiki. Have fun. 