Apple was rumored to be negotiating with them a couple years ago, but they were unable to reach a deal. Apple never had any interest in buying them, all they might want would be acquiring/licensing IP. If they bought them outright, they'd be responsible for existing customer contracts and support which could run for years. Basically they'd have to keep operating it as an independent company, which isn't what Apple does with its acquisitions.
A Chinese owner would be good news / bad news for Apple. It is good news because Chinese companies almost never fight IP cases off their home turf, so Apple is unlikely to be bothered outside of China. The bad news is that Chinese courts are notorious for enforcing weak cases against foreign companies, so they'd probably lose even if Apple doesn't use Imagination IP (FWIW the hardware capability claims they're making in their developer docs include some that have never been done in Imagination GPUs, so it is by no means certain Apple's new GPU is infringing)
Apple will probably end up having to pay the 'China tax' either by purchasing a perpetual license from the Chinese company for the IP or letting the court dictate things, but most likely they'll be off the hook in the ROW.