If the IC and the peripheral components it connects to (exclusing the power supply) are connected to nothing, the connection you propose is fine. That would be the case if the IC is a microcontroller and its peripheral components are leds, and isolated buttons.
However, as soon as you connect some external devices, your negative power supply is likely to become a problem. That's especially true if your power supply is connected to the electrical grid (mains): perhaps the ground of your supply is connected to earth, and the ground of the other supply of that external device too. Now when you connect the GND of your IC (the -5V output of your PSU), and the GND of that external device (also the ground of its power supply), you actually short-circuit your power supply, thru the earth connections of both power supplies. Even if the ground output of one or both supplies is not earthed, you might run into problems due to capacitive leakage from mains to ground output, and power supply noise, which turns into a signal; e.g. in an audio or video context.
So in summary: for an overall system with at most one mains-connected power supply, what you propose is fine (and very justifiable if a negative regulator has better characteristics than a positive one). Problem starts when your power supply is mains-connected and you connect the GND of your IC (the -5V output of your PSU) to the GND of another system that has a mains-connected power supply.