I'm a musician and I'm incredibly confused by this point. Music instruction cannot possibly be effective without a visual component, regardless of whether it's a solo instruction or a group. An A/V method with a bit of latency is almost always going to be superior to audio-only.
Even just touching strings in different ways can produce wildly different results; think playing a harmonic note on a bass guitar, which is how you get such a low-sounding instrument to play a high-pitched note. How you blow air through your horn can greatly change the timbre and mood of your music.
There are a lot more examples, and they are all difficult to correct if you aren't able to see what the musican is doing.
I suppose blind people will never be successful with music.
Blind people are perfectly capable of learning to play music. Blind people and non-blind people alike can learn on their own, or seek out instruction. It is the latter that we are discussing here.