You are right. In classical Newtonian Physics (with use of general relativity) a dark star is a 'star' whose escape velocity is equal to that of c (and/or the speed of light). So a 'dark star' is analogous to a 'black hole'; due to the fact that any light emitted by the 'star' as well as any light that comes in contact with the 'star' is immediately absorbed back in (because of its immense escape velocity and the 'stars' gravity)...
the main difference between the two is the way they emit radiation. Dark stars emit indirect radiation while black holes emit radiation through what is known as Hawking radiation. There is also another difference that is less pronounced: it is related to how they bend light ~ it's more of an argument of the modern theory vs classical Newtonian physics and the way space-time is inferred...
I could go on but yeah...
tl;dr: a 'dark star' and 'black hole' are basically the same thing.