Here’s my experience although it was at uk Hilton’s and 4 years ago....

1) I found that there was nearly always a non refundable deposit to pay however most of the time this was waved as a diamond member.
2) didn’t seem to effect upgrades, I found this to my surprise.
3) obviously dogs are not allowed in the bar/executive lounge or restaurant but on one occasion I was told I was welcome to bring my dog to breakfast with me, I didn’t as I thought it was unfair on others.