There is no general rule as to what DCR should be. Typically, DCR will be around 4 ohms or less for drivers with nominal impedance of 4 ohms and 8 ohms or less for drivers with nominal impedance of 8 ohms. DCR is the resistance of the winding using direct current. DCR will be lower when the voice coil has a larger conductor size or fewer winding turns. The impedance of the speaker is measured over the frequency response of the speaker. Impedance varies as the frequency changes because impedance is a combination of the resistance, inductance, and capacitance of the speaker/driver.
Measuring DCR will tell you if the voice coil has an open circuit. That is, checking DCR is most useful as a continuity test of the VC. Unless you know the DCR for a specific driver, you cannot draw any other substantive conclusions just from knowing the DCR. If you have another identical driver that is known to be good, you can measure that DCR and compare it with the other. If one is good and the other has substantially the same DCR, you can assume that the other is good, too.