No. Many critics who make this claim this point to a single photograph in which an alarm clock was removed from a photo (Lodging Interior - Piegan, volume 6). However, Curtis scholar Herman Cohen Stuart has identified examples of modern western influences in photographs in all twenty volumes, including automobiles, housing, and clothing. It is more likely that Curtis had the clock removed simply because it was visually distracting and was not in keeping with the pictorialist ideals of making timeless photographs. For more about this issue, please see Herman Cohen Stuart, Unraveling Edward S. Curtis's The North American Indian (Cambridge Scholar's Publishing, 2023), and Shamoon Zamir, The Gift of the Face, Portraiture and Time in Edward S. Curtis's The North American Indian (University of North Carolina Press, 2014).

No. According to two of his children who traveled with him after they became young adults, they never saw him use any regalia or objects that weren't offered by the people he photographed. It's true that some regalia appears in his photographs mutliple times or, more rarely, clothing from a particular Native Culture appeared on people from a different culture. It is thought that these were presented by the people Curtis photographed.

Curtis was photographing using a large format view camera. This style of camera, which is still used today, employed a film holder that would be inserted at the back of the camera once the subject was in position. However, the "film" used by Curtis was a glass plate negative. In Curtis's time were produced by Eastman Kodak and had a film speed of ASA 14. Most modern day sheet or roll film used today has a film speed of at least ASA (ISO) of 100 and often more. The result of using this type of film, and all photographers of Curtis's time were using this or something very similar, was that the exposure time was fairly long. It was not possible to simply point and shoot as we would today since the film was too slow. As a result, people had to fix their facial expression for several seconds. In addition, Curtis wanted his portraits to show the dignity of the people he photographed. Their facial expressions often reflected the difficulties they had experienced and their dislike for what had happened to their cultures due to treatment of the federal government and the incursions of white settlers on what was once their lands.

This is the result of the orthochromatic film that was commonly used until the 1920s. This film is sensitive mostly to the blue end of the light spectrum and not sensitive to red wavelengths. The result is that anyone who had darker skin tones was rendered as very dark when printed.

There are two types of black and white film, orthochromatic film and panchromatic. The difference in the two films for this question is their light sensitivity. One benefit of using this type of film emulsion is a red safelight may be used in the dark room for loading the film and for processing the film as well. Panchromatic film is sensitive to a much wider light spectrum and renders reddish things in a more accurate way. Unfortunately, the film must be loaded and processed in total darkness.

For a more detailed explanation see here: https://filmphotographyproject.com/content/howto/2018/07/panchromatic-orthochromatic-film/