What do you mean by "suffering from DC power loss"?
Are you referring to a problem with the DC input of VFD, which you were using for solar? And you want to move PV panels from VFD to inverter, using that together with VFD to run pumps?
Or do you want to use solar to power the inverters for a different load?
Possibly output of VFD, with motor connected, would form a grid. However, "Variable" frequency drive would be outside the 50 Hz or 60 Hz +/- 0.5 Hz (or so) range GTI inverter accepts under some conditions.
AC side input port of VFD, no grid would be formed. Generator, when running, would form grid, but isn't designed to receive excess power like from GTI inverter. If your GTI inverter can use current transformers for zero export, that might work; up to 100% of available PV would be added to AC power, relieving load from generator. In this case, generator needs to continue delivering frequency in-spec so GTI doesn't go off-line. If GTI performs frequency-watts, that might respond to such frequency variations, an additional way to curtail production in order to match load.
I'm not sure what you're trying to accomplish, since it seemed like generator + solar was meeting pumping needs. A drawing of how you're thinking of connecting equipment and explanation of how you want it to work would help. But probably different equipment designed to be grid-forming would be best.