I'll be fair...from a business standpoint, yes, Em and the Interscope camp should have credited them. Not so much saying Em had to personally reach out to them, but someone at the label could have reached out or even possibly given them sample credits on the CD.
Still, the way they react is to throw a diss at Eminem? Obviously Eminem liked the song so much that he referenced it on one of his most promoted songs of this CD. Why not just do an interview to get the word out that they felt a bit "disrespected" that Em/Interscope didn't reach out. Responding by throwing a diss track at him is silly and plain dumb.
When Rap God came out I went on their Twitter and they were giddy like school girls about the reference. They even @ Eminem thanking him and RT the hundreds of tweets of fans talking about Eminem using their beat. Those tweets have since been deleted of course. So I call a bit of bullshit that right away they were offended, they freaking wrote him a thank you tweet hours after Rap God dropped.
Anyways, their point is valid, but because of the way they went about making their point then Em should really just say fuck them now. No response (how the hell does it benefit Em to waste time dropping a diss record specifically for HotStylz? HotStylz), no acknowledgment, just keep it moving.