The simple answer is no. It would take a short book to explain all of the issues, and I wish I had the time to give you the solid explanation.
Here is the short version.
The modern PWM AC drive (see link
http://www.otherpower.com/images/scimages/2819/AC_power_section.jpg ) is designed to accept a fairly stable line voltage. If the voltage fluxuates beyond the limits (usually +10/-5%) then the drive will protect itself and the motor it is running, by shutting off all it's output transistors and tripping out. If you were able to by pass all this trip circuitry, (not a DIY task)you could get the drive to provide a stable, controlled frequency, however because the DC "Buss" section is unregulated, the output voltage would be unregulated as well. Also, the output of a AC VFD is a noisy Pulse Width Modulated waveform, not a sine wave.
DC drives (SCR type) have the ability to accept the "wild DC" feed it back to the power line. This is called a regenerative DC drive, however the power it feeds to the grid is usually a poor power factor (depending upon phase angle of conduction) and harmonic rich. It would take some sophisticated filters, and active PF control to produce a good quality power, efficiently, back to the power line. Hence the reason for the "grid tie inverter", they have all this extra filtering, and PF control built in.
Both AC and DC motor drives perfom their functions very well...they control the speed and torque of electric motors. Without extensive modification, they do not make good power conditioners.
On a side note: If I can ever stop working 80 hours a week, and traveling 29 out of 30 days a month, I will try to modify both types of drives, and a 3 phase SCR heater control to show what the pro's and cons are of all types.
I am envious of all you folks on this board who have time for their projects...keep posting, I live vicariously through you! :-)