Ok I just checked it out.. It doesn't just require a DTV login if someone is already subscripted to NFL Sunday Ticket.. they also have to pay for NFL Sunday Ticket TO-GO.. It allows you to watch games on your PS3 (Xbox too maybe?), smartphone or computer..
You can add TO-GO to your original subscription for 5 payments of $9.99 is what the FAQ says.. When I looked at the order page, it was very confusing.. It had two choices.. $9.99/mo for 5 months or $45.99/mo for 1 month.. which I'm guessing means the $9.99/mo for 5 months is some sort of deal where you are locked in for a year after the 5 months..
So yeah, the only way you'll get someone's log in is if they are your family member or something because of the fact you actually have to pay quite a bit extra to use the App as a normal NFL Sunday Ticket user wouldn't have access to the app.