The tetragammon is one of those words that never really should have vowels with it. Derivatives actually show that it was Yeh (Yehoshua) although it could be Yah (yashua) but I seriously doubt that Tiberian or any other modern Hebraic pronunciation is 100% exactly like the Jews of antiquity spoke it. Hebrew, like Egyptian (Coptic) and Latin and Greek, all seemed to have shared a common phenomenon around the 1st century BCE that forced the hard sound "b" into a softer "v" - a common linguistic trait also occurring in the Germanic languages (cf. pater and father). So there is no telling exactly how a word without vowels ever really was pronounced, because like all languages, and animals too for that matter, they (semitic ones) evolve.
As for the Tetragammon in writ, I've raised the question on my forum, noticing that it was definitely treated with some special treatment, often written in palaeohebraic or even as merely dots to represent the word. A very interesting word indeed! And what does it really mean? No, contrary to popular opinion, it doesn't "really" mean I AM, in fact, it probably was only the name of one of the local Canannite gods of that pantheistic society, the same with El and Ashura, that was chosen to be maximised into its current status today: infinite. The same happened to Zeus and Jupiter, if you recall the Socratic dialogs, and Socrates himself had to show that their very own scripture contradicted this sentiment. So too will you find this idea nil in the Hebrew Scriptures that you call yourselves the "Old Testament."
I don't think it matters which vowels you put in.
