No, off site hotels DO NOT get the FOTL perk - but yes, if you have the HP package booked, even at an off site hotel, and are arriving between 5/28 and 6/18 you will be given access to WWOHP - but it must be the HP package (breakfast at Three Broomsticks, Commemerative ticket, etc).
Pete
I called Universal last night and complained because I booked a package back in January. I will be staying on site and my tickets run through May 29th. I received an email about the Harry Potter package and called Universal in February to inquire. I was told that I did not have to change my package. Since I already had an "on property" packaged deal, that I would be fine.
When I explained this to guest services last night, I was told that as long as I had a packaged that was "On Property" and booked before yesterday that they would honor my ticket and I could get into HP.
I don't think anyone has heard the end of this.