Factored into your question are quite a few subquestions, all aimed at figuring out the question of how Japan and China perceived Okinawans, and internal Okinawan identity from roughly 1940 - 1960. As you might expect, there's some variation over time, and this is a question relevant to many people in Okinawa today.

As you likely know, Okinawa was the self-ruling Ryukyu Kingdom until 1872, and had a king until 1879, when he was removed by power and given a title of nobility subordinate to the Japanese Emperor under the reorganized system of peerage. The question of whether this was legitimate and would be uncontested by China, who also had interest in the Kingdom as a tributary state under suzerainty, was open until the First Sino Japanese War in 1894-95, when Japan's annexation of Formosa (Taiwan) expanded the frontier and put to rest any notion of Chinese military intervention leading to their annexation of Okinawa, or a restoration of the former kingdom's sovereign rights.

In the late 19th and early 20th centuries, there was plenty of debate by scholars in Japan over whether and to what degree Okinawans could be considered Japanese, generally in the service of justifying Japan's control over the island or later the unequal treatment of Okinawans in relation to "pure" Japanese. From an Okinawan vantage point, they tended at best to assert a patronizing idea that Okinawans preserved a more primitive form of Japanese language and customs, and being a virtuous but less developed race, was akin to the Western noble savage.

Mostly, however, this academic debate was largely irrelevant to the daily realities of the average Okinawan, whose lives lagged decades behind the mainland Japanese in economic and technological sophistication, and in many cases people lived in farming villages not particularly different from the pre-industrial and pre-modern ones that could be found prior to the Meiji Restoration, even as late as the Battle of Okinawa itself.

This is not to say that Okinawa was a total backwater. Elites in Okinawa congregated in Shuri and Naha, and had their own internal debates over what it meant to be Okinawan and their place under Japanese rule (and later, American rule). Prior to and during the First Sino Japanese War, the Okinawan political class was split between the pro-Japanese Kaika-tou Enlightenment Party, and the pro-Chinese Ganko-tou Stubborn Party, and at stake was the future of both Okinawa and Okinawan identity. (Yes, those are the actual names.)

It's contested vigorously by Masahide Ota that Okinawa lacked any sort of real political consciousness until the 1910s, however, helped in particular by the establishment of a local newspaper in 1893 (the Ryukyu Shimpo). Any understanding of an internal sense of Okinawan identity and allegiances in the upper classes must necessarily be bolstered by a knowledge of the opinions run in this newspaper, and while it's true that the Ryukyu Shimpo very strongly favored Japan and Japanization, a certain view of the concerns of their opponents could be seen by the choice and manner of topics discussed.

Indeed, Imperial Japan instituted a strong program of cultural assimilation on Okinawa that is widely seen as the forebear for the programs instituted in other colonial possessions such as Korea, the Philippines, and Taiwan, seeking to erase indigenous language and customs and replace them with more "enlightened" Japanese versions. There's no doubt that the Okinawan families who raised more sons acculturated in a Japanese style found greater success in local politics and business, and were the only ones who had any hope of finding inroads to the more prestigious and wealth mainland.

It must be remembered, however, that these elites were caught between the powerful forces of the Japanese government urging assimilation on the one hand (who endowed their Tokyo-appointed governors from the mainland a set of harsher laws and powers to wield exclusively in Okinawa for a number of decades), and Okinawan people who were slowly becoming aware of the severe difference in social conditions both between people with the prefecture, and between the prefecture and mainland. As a result, you can see a stunning relative lack of discussion in the Ryukyu Shimpo of things like civil rights and freedoms that were taking the mainland by storm in the Taisho era. Even in subordination to the pressure of assimilation, the non-Japaneseness of the elite classes of the Okinawan people could be seen in their different concerns and aspirations in relation to those of mainland "pure" Japanese.

The power and intensity of Imperial propaganda during the intense militarization of the early Showa period should not be understated, of course. This deeply muddies the question of an internal sense of Okinawan identity, but there can be no question that a wide range of views existed such that it's impossible to encapsulate the answer in a simple, "Yes, they were Japanese," or, "No, they were not Japanese." It's intensely difficult to understand and relate to the complex feelings that are evoked in people who live under a system in which they are essentially colonized.

What can't be doubted, however, is the widely held opinion by Japanese people that Okinawans, whatever the opinions of scholars, might be related to Japan, but were definitely not of the same status as mainland Japanese--and many considered them to be of a different race entirely. Reports of individual discrimination are numerous throughout the Empire. Okinawans did acquire a curious status in farther flung colonies, somewhere between pure Japanese elites and the truly subordinate local people. But by and large, whether on Okinawa or off, Okinawans suffered discrimination, of which they were surely aware, and may have caused some to feel alienated and others to feel pressure to more fully prove their loyalty as citizens of the Empire when they were urged to mass suicide. It also was a factor in the carnage inflicted both directly at the hands in Japanese soldiers, and indirectly in the economic neglect and ill-prepared nature of the defense of the island. As one particular example, 11 years before the battle, in 1934 Colonel Ishii Torao, Commander of the Regimental District in Okinawa and thus in charge of military issues within Okinawa, sent a report to his superiors urging the stockpiling of essential goods such as food, as he correctly predicted there would be widespread famine on the island if supply lines were disrupted due in large part to the economic conditions in the previous decades which turned Okinawa's economy to be based almost solely on sugar production, and the continued lack of development on the island. This recommendation was ignored, and both civilian and soldier alike starved in the battle, with many accounts of Japanese soldiers enacting violence on Okinawan civilians in order to get access to whatever food they had available. Even worse, prior to the battle, Hosokawa Morisada, son-in-law of the less hawkish leader Konoe and who was secretary to Imperial Prince Takamatsu, Hirohito's brother, wrote in his diary, Information Never Reaching the Emperor, "On top of such miserable conditions [of the bombing and shelling in 1944], the [Japanese] troops were totally undisciplined and had confiscated a few houses still standing, behaving as if Okinawa were their occupied land. They had no discipline--forcing the residents to live under the same roof with the troops, making use of civilians' possessions as they liked, and raping women."

Discriminatory attitudes towards Okinawans also affected strategic considerations, as well, and the ambiguous status of Okinawa as Japan and not-Japan was reflected in perceptions of the battle. Many historians consider the Battle of Okinawa the only land battle from WW2 to have been fought on Japanese soil, and it certainly increased the feeling of threat and fatalism on the mainland when it was lost because of that perception. At the same time, while leaders were hoping to fight a "decisive" battle to protect the home islands of Japan, Okinawa was seen as a necessary sacrifice for the good of the Empire, and strategy was intentionally formulated to make it a long, costly, bloody battle to stall the Americans for as long as possible in order to buy time on the mainland to prepare for that ultimate battle, where there would be no sacrifice, but victory or death. Such strategies along with plans for Taiwan were formulated under Operation Tengo, as opposed to Operation Ketsugo which focused on preparations for the mainland, showing a clear division in class and value between the main four islands and Okinawa, relegated to the same status as Taiwan.

This attitude continued to be reflected after the war, too, reaching even as high as the Emperor, as he directly and in secret offered Okinawa to MacArthur as a permanent US territory in exchange for concessions on the mainland.

As far as the Americans went, the short version is that while they considered Okinawans civilians of the enemy during the war, they were aware that differences existed, and even brought Okinawan-Americans to communicate in the endangered Ryukyuan languages during the battle, to some effect. As one moving testimony archived in the Okinawa Prefecture Peace Memorial Museum notes, "We left our hiding place in the tomb because the Americans spoke our language. My uncle said that nobody who spoke our language could mean us harm." This is in direct comparison to Japanese soldiers who executed speakers of Okinawan as potential spies.

After the war, American military administration sought to encourage and highlight differences between Okinawans and mainland Japanese down to as a political strategy in order to consolidate their control of their new territory. As far as the individual soldiers' attitudes go, I unfortunately don't have much knowledge on that topic. I hope the rest suffices.