But in all reality, they don't really play all the mainstream artists. Like Adele and Katy Perry are like staples on the format, but they snub Britney Spears almost entirely. Gaga is more of a mid-grade. They don't spin her as soon as she releases a single (and definitely not as quickly as Katy or Adele) but they don't snub her entirely like they do Britney.
Her music fits Hot AC to an extent. Something like "Teenage Dream" and "The One That Got Away" fit it. Katy is a rarity. She has done well on that format and AC.
To be honest, I think they cling to Katy Perry more because she's much more "likable" by the general public than Gaga. Katy doesn't have the explosive polarizing reactions that Gaga has.