Its supposed to be pronounced like the Ch in Chimera. I reject that reality and pronounce it like Chimney.
I tend to do as well. It's just easier. Hell, originally wasn't Dunmer pronounced "DOON-mare?" We can just call it an Imperial mangling of the original Aldmeris or we can just say this way is easier, but however you slice it that's now even how people in the games say it.
As for [numinit], it is basically just a way of avoiding the Lovecraft Pitfall of spending a lot of time describing how indescribable something is, which can get really tedious really fast. Instead, we have a single not-word to carry the idea across.