I think indentured servitude is the wrong way to look at this. The key difference is that the investors don't dictate that you need to achieve a certain level of returns, or that you pursue a certain line of work. Instead you're still free to do whatever you want.

Since these contracts don't impinge on personal freedom, they should be legal. And I dare say that any number of highly motivated and intelligent people would jump at an opportunity like this (myself included), especially with the buy-out clause.