Is it ok to use voltage dividers instead of voltage regulators when adjusting reference voltages for opAmps?
Yes, you can use voltage dividers for setting reference voltages.  There are a few questions that you need to answer, though.

1) How accurate does the reference need to be?  Will the temperature coefficient of the voltage divider components have any effect?

2) What feeds the voltage divider?  Does that have sufficient accuracy and stability?

In general, what you are asking is generally considered to be standard practice.  The reason this is the case is that many times, the reference voltage that you need either needs to be variable (to allow for calibration / setup) or the voltage that you need as the reference is not available as a standard part.