It's something that happens in the VGM industry from time to time. One of the best known examples is Hideki Naganuma going under the alias skankfunk to compose a few tracks for the anime Air Gear (and sound directing the OST as a whole), he admitted to doing this due to not being allowed to work on projects outside of Sega. Another more obscure case that I know of is Satoru Kosaki; back when he was an in-house Namco composer, he used the alias Shinji Ikeda to compose the score for the Munto 2 OVA (and did leave Namco to join Monaca not long afterwards). There's probably other cases too.
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