I didn't see the the article as so much giving Dick a pass, as it explained that Dick avoided a lot of the visual issues and intricate details that ended up causing problems in the Amazon series. He stuck with what he knew and didn't provide unnecessary information that could have caused accuracy problems.
Being an alternate history, Dick created a completely new situation, a defeated US occupied by Japan, and as such it's hard to criticize it for accuracy. Even when he does things like have a down-do with a kimono, that could just be an alternate history detail that conveys a cultural mix--a western hairstyle with traditional clothing.
The standards back when Dick wrote the book were different. He was a not-famous genre writer whose books were published as paperbacks, and a really high level of accuracy wasn't so much demanded back then for books that were not highly regarded anyway. Plus it would have been difficult for many of his readers to detect any problems so a higher level of accuracy wouldn't have made a difference to the reader.
Dick typically wrote very quickly. He wrote one draft, really fast, so that he could get some money. He was always severely short on money. This is the only book of his that he had the luxury of spending more time on. He wrote several drafts, and it has therefore a more polished quality. But he didn't have the finances or the incentive to spend a lot of time researching it. Honestly, I thought his accuracy was better than the vast majority of American books I've read with Japanese protagonists. Compare it to Michael Crichton's Rising Sun. His depiction of Japan and Japanese culture was dismally bad and offensive, despite him having as much money, leisure time, and access as he wanted, to write a really well-researched book in 1992. I believe Crichton DID think he'd written a well-researched book, but no, no matter how much research he'd done, he misunderstood it. This was a case of him reading what he wanted into the sources he found, rather than not having access.
Have you read The Chrysanthemum and the Sword? It was the gold standard in 1961 for an ethnography of Japan. And today, while it has some good information, it also is quite creaky and outdated. I think what Dick wrote would have passed for incredibly accurate information about Japan, to a 1961 American crowd, as most Americans' understanding of Japanese society was quite different and, to our eyes, inaccurate. Dick avoided a number of the cringe-inducing stereotypes about Japanese people that were so prevalent in 1961. The book is vastly superior to, for example, You Only Live Twice, the James Bond novel published in 1964. If you read that, you can easily discern the exact books that Ian Fleming read about Japan before writing the novel and cringe at the simple details he gets wrong, like saying that Japanese people wear masks to avoid being exposed to the germs of others (it's really the reverse. People who are sick wear masks so they won't transmit their cold to others). And he gets a lot wrong. Dick seems to have steered away from the misinformation in sources like "Know Your Enemy: Japan", which was perceptive of him.
Dick had a number of Japanese-American friends, and it was from them that he got a lot of his information. That really helped I think to enrich his book. The San Francisco Bay Area had a large Japanese-American population, including many people born in Japan. So in that sense he had more access to people who could help him with cultural and linguistic issues, than many people do today.
One thing I would point out that Dick either ignored or didn't have a lot of information about, were Japanese wartime atrocities and what it was like to live in the Japanese empire. His depiction of the Japanese occupiers was relatively benign as compared to the reality faced by people living in Japanese colonies. Would Dick at that time even have known about Unit 751, for example? Perhaps it was a deliberate choice on his part to ignore it because that's not the story he was telling, or perhaps he didn't know about it and so didn't even know the right questions to ask. He definitely would have known about The Rape of Nanking, for example, but that, too, was not the story he was telling. My opinion is that Dick wrote much more believable, complex, and accurate Japanese people than he would had he based his people on more abstract research from books and films.
So I think overall, there were many venues through which Dick could have researched Japan--not as readily, quickly, and cheaply as he could today, but still, it wasn't like he'd be completely blocked from any knowledge, and he appears to have taken advantage of the sources he could access, beyond the limits of what would be reasonably expected of a novelist of that time. But even had he done more research, he might not have increased his knowledge--he might have increased his misinformation as much as his information, given what was available at the time. But Dick was creating a not-accurate Japan as a deliberate literary choice, anyway. He was an admirer of Japanese culture and wanted to convey certain aspects, as well as to contrast his alternate-history Japan with his alternate-history Nazis.
In contrast, the Amazon series, being created by hundreds of people and in the 21st century, would have had a far greater abundance of resources with which to research information than one lone, poverty-stricken writer would have had in 1961. But they also had to do set-dressing, so they had a far more complex world to design than Dick did.
If your question is whether or not Dick could have done research on Japan, I can attempt to answer that question, albeit purely circumstantially.
They obviously didn't have Google and Wikipedia in 1961, but they did have books and libraries. PKD grew up in Berkeley and briefly attended Cal before dropping out, so even if his local library (he lived in Marin County at the time TMitHC was written) didn't have what he was looking for, he would have at least known that the Cal library existed as a resource. He also still had friends at the University, so he would not have felt unwelcome visiting, or at least no more unwelcome than he felt anywhere else due to his crippling paranoia, agoraphobia, and schizophrenia.
So the question is, were there books about Japanese culture, published in the US by 1961, that he could have gotten access to if he wanted. After a brief search on WorldCat, here is a short (certainly not comprehensive) list of books on Japan that one could reasonably expect to find in UC Berkeley's library in 1961:
Yuki Yamamoto: Approach to Japanese Culture, 1961.
Edward Seidensticker: Japan, 1961.
Daisetz Teitaro Suzuki: Zen and Japanese culture, 1959.
Robert Schwantes: Japanese and Americans; a century of cultural relations, 1955.
Lawrence Ernst Gichner: Erotic Aspects of Japanese Culture, 1953.
Ruth Benedict: The chrysanthemum and the sword : patterns of Japanese culture, 1946.
Jiro Harada: A glimpse of Japanese ideals; lectures on Japanese art and culture, 1937.
InazoĢ Nitobe; Yasaka Takaki: Lectures on Japan; an outline of the development of the Japanese people and their culture, 1936.
Thoburn T Brumbaugh: Religious values in Japanese culture, 1934.
I'll add that Zen and Japanese Culture is cited in the acknowledgements of TMitHC, so he undoubtedly read that. Chrysanthemum was also a very influential study at the time, so even if he never read it or even heard of it, it played a huge part in shaping the general post-war American perception of Japanese culture.