Jim Hill is a Disney blogger. He's been in the biz far longer than most--today you can't swing a churro without hitting a half-dozen self-proclaimed insiders.
I can't give you chapter and verse on his credentials. I don't believe he was ever a Cast Member--he certainly is not at the present time. There was a famous story from about 5-7 years ago where
Disneyland management had him removed from the park for trying to lead his own guided tour for a group of people. National news picked up on that one.
Hill has written some great stories on the history of Disney attractions and parks over the years. Unique stuff that you haven't heard repeated a dozen times over.
He does have some inside sources and will discuss future plans at times. That's usually where his critics focus their venom.
Personally I give Hill a lot of credit for climbing out on a limb--when he writes a story about future changes to the parks or attractions, all of the credit / blame falls right on his head. These days most "insiders" prefer to hide behind screen names and guarded forum identities. Wish I had a dime for every mention of the Monster's Inc coaster or character meals in Adventureland.
Anonymous forum poster is allowed to just say "well, it was going to happen but plans changed." Meanwhile Hill is raked over the coals for being the victim of similar changes in plans.
I guess that's the risk people run when they deal in rumors. Personally I just happen to find the hypocrisy amusing.
His writing style is often condescending so that doesn't win him any fans. About 3-4 years ago his website was far more interesting when he was regularly posting historical Disney info.
Hill is what he is. Anyone who deals in rumors is going to get burned over time because plans CAN and DO change. Often. Personally I don't find him to be any less accurate than "PaulCM2001" or any other mystery forum poster. And Hill is one of the few willing to put an actual name and face to the things he writes.