Yes, HHN will be in both parks, BUT only certain portions of each park will be open. So, you won't be able to ride everything.
If you go to the HHN website and check out the event map it will show you the portions of the park used for HHN. It hasn't been made official which rides will be open, but it looks as if Marvel Super Hero Island and Suess landing are the only portions of IOA to be used, and only the New York, San Fransisco, and Production Central areas of Universal are going to be used.
I'd assume most attractions in these areas will be open. But if it is like last year, a lot of the rides had long lines. And with all the haunted houses (7!) this year, I doubt if there would be enough time to do it all.