I have no idea why Universal calls these 'participating' hotels, as they certainly don't participate in any of the perks that you get when you stay on-site, especially the FOTL.
Other than that, there have several satisfactory review about some that you listed. I am sure others will jump in here and be more specific.
We stayed at the Sheraton Studio City and I would definitely stay there again. Rooms were clean, beds comfortable, the staff was fabulous and its about half a mile from US/IOA. I also loved the theming of the hotel.
I have no idea why Universal calls these 'participating' hotels, as they certainly don't participate in any of the perks that you get when you stay on-site, especially the FOTL.
the reason they call themselves universal partners I am afriad your right is because of the shuttles and also the fact they give you a card holder for your room key that gives you a 10% discount on select Universal stores and citywalk restarants.
We stayed at doubletree on major blvd and they are universal partners and never tried using the discount at resturants but did use at universal store and did save a little.