Facing the same issue.
I have LG OLED65B6T-T with software version 05.30.60 and Web OS version 3.3.4-4315 (dreadlock dharug)
Hotstar has tweeted to me as well that their app won't work in versions below WebOS 3.5.
Is there a possibility of LG updating its LG WebOS to 3.5 from the current version?
Someone answer please.
Edit: The other thing that baffles me is that when AltBalaji, Spotify and Zee5 apps can be made available then what happened to Hotstar? Why can't Hotstar's developers create an app for versions lower than WebOS 3.5?