MOBS for online/external servers are a feature that is currently under development. 

Basically, MCPE is trying to catch up to the PC version.  Hence, the game updates : )  For now, they’re unavailable for ALL online servers under ANY service.  We're waiting for these features as anxiously as you are : )  As soon as they’re available you'll see them in action, in your MCPE world! 

Here at PotpotsieLLC, we are on the cutting edge of what is available as far as MCPE external servers go.  There are differences between these external servers and local servers, but their programers are working to make MCPE features identical to the latest updates of the game.  

Moo, moo!  Cluck, Cluck!  Gurgle, gurgle!  Hiss, snap!