I'm not sure that being a member of the "Reiki Alliance" is any guarantee of anything either. From what I hear, the members of this group charge pretty high fees for attunements. I know it is possible to find a teacher/Reiki Master who DOES have the proper lineage and who doesn't charge an arm and a leg.
Now, I have read one commentary on the symbols where the individual says that the symbols themselves are not all that important, that they are only "triggers" and do not "carry power in themselves", that they are similar to the bell that Pavlov used to "condition" his dog. I don't agree with either the idea that they are just triggers, nor do I agree with the opposing idea that they "carry power in themselves". I noticed, during my very skeptical initial foray into Reiki, that the symbols were important, but not for the usually assumed reasons - either as triggers or as something that is powerful in and of itself. After a lot of observation and experiment, I hypothesized that the significance of the symbls was that they are like something that "communicates information" into one's energy field, that they more or less "etch psychic circuit boards" in one's energy field.
So, in the ideas that I formulated about them - and in the terms the C's described them - it IS important to get them as accurate as possible.
The symbols that were published by Diane Stein are gross distortions of the original symbols, and that's not to say that the Reiki Alliance gang - and even Takata herself - had a real clue. At least, however, Takata tried to convey them intact in form and stroke order (which is important).
I don't know who came up with the story that the symbols are Tibetan - they are clearly not - and I think that it was Takata herself. I have read the theory that the reason for this idea being propagated is that it's like the game of Chinese Whispers, where you tell something to the person next to you, and they tell the person next to them, on down the line, until, at the end, it bears no resemblance to what was originally said.
As a Buddhist, it is said that Usui would have had knowledge of Shuji which is the Japanese name of the "seed characters" written in the Siddham of the Sanskrit script, and which are used as attributes for deities. So he may have talked about this Sanskrit "idea" when teaching about the obviously Japanese characters he was using, and he may also have talked about Tibetan characters in the same context: to give an example of the way something is used.
You can visit this website: http://www.geocities.com/fascin8or/reiki_symbolsP.html to see what appear to be accurate representations of the Usui symbols. He also includes pages that show the various other representations - corruptions - of the symbols so thaty you can see what others have done to the "circuit" creation process.
The above linked site seems to have some very good information, so perhaps it might be useful to write to the author and inquire about Reiki masters from him?