I doubt Gaga hates Demi, that incident was really minor and Gaga hasn't talked that much about Demi so she doesn't need to worry. Perhaps a little bit of time will delete that awkward moment.
And to the people saying Gaga hates Katy, remember that an artist fans do not talk for the artists themselves. Some Monsters hate Katy but Gaga herself is very neutral about her I think. I don't think she's a fan but their relationship is not that bad.
I will not let you all jump on that Demi hate bandwagon again. Go do something with your silly and empty life bitches and let Demi alone. She's more succesful and has way more talent and money than you'll ever dream of.