You need to ask the person/agent you are dealing with. If it is installed it will probably have been disconnected so you will have to pay for it to re connected.
If you plan to install Sky or Cable yourself at a later date then you will probably need a letter from the Owner/Agent agreeing to this before the suppliers will go forward with your application
I've lived in two rented places and neither had Sky or cable but I had it installed myself at both places - cable, so I didn't attach a dish to his house or anything. I didn't need a letter from the landlord (in fact I don't even think I asked him...).
At the end of the day it is increasing the desirability of his property for the next person if there is a sky/cable connection already installed!
In my past rental places it has always been a condition of the contract that I get the landlord's permission before installing anything of this nature as it requires work to be done on the house (holes drilled etc.) if the supply is not already in place.