There is plenty of evidence, and usage of, "inner beings" in the psychological and spiritual spaces. Inner child work, deep spontaneous imagery, spirit animals, angels, etc. This simply seems another way of looking at that kind of phenomenon. I have done a lot of similar stuff, though I tend to interpret it within a psychological model, and I have more than one of them.
Whether these tulpa are subconcious imagery "come to life," spirits, angels, or simply imagination, I find it can be a very creative way of dealing with issues. As long as your relationship with your tulpa remains open, honest, and grounded in good sense, I think its pretty interesting, and has potential to be a path for personal growth.