They have 6 "Official Hotels" which are 3rd party hotels located within the resort. 2 of them are American chains (Sheraton and Hilton). They are connected to the parks by monorail. I believe you can walk to the parks as well.
It is not officially a good neighbor hotel but MyStays Maihama is within walking distance to the resort
I will say that I have been planning, since around April or May for our trip next November 2020.... and what I have found that Japan takes quite a bit more planning, and researching than we went to Paris last year.... Transportation being in on top of the list, figuring out the trains, what passes you will need, as well as gauging the distance between areas of interest, and time frame that it really takes to get to a area... Then airfare, hotels, and really what you want to see and experience in Japan... everyday, I add more and more to the list... then wanting to really be able to take in everything at Tokyo Disneyland... is a whole other game... its really like planning 2 trips... and meshing them into one cohesive plan... I have about about 100 pages of notes in my trusty notebook, and about the same in my word pad... the thing is I haven't really started the "real plan"....
I stayed at both the Sheraton and the Hilton on my last trip, Sheraton for a night, Hilton for five. Both were very nice hotels, although I preferred the Sheraton.
One thing that I thought was nice about the Hilton was that Hilton Honors members (free to join) got a free buffet breakfast every morning, at least as of June 2019. It was a nice mix of Eastern and Western options.
Both are easy walking distance to the Monorail station, although they both also have shuttles too. Then it's one monorail stop to DisneySea, two to Ikspiari (and Maihama Station), and three to Disneyland. You could walk to Disneyland if you wanted to, but you'd need to take the monorail to DisneySea.
I will be visiting Tokyo Disneyland and Tokyo Disneysea for 2 days at the end of November so see the Christmas decorations and staying at the Hilton Tokyo Bay and use the monrail to Disneysea and walk to Disneyland.
Well, you could walk it if you're in the good neighbors but there wasn't a major direct pathway. Check google maps and look at it to verify. Monorail was really close to the Sheraton, and like previous poster says, there are shuttles too directly from the lobby entrance. Was nice to ride the monorail to get a view of the area, but there is a nominal charge to ride it...