The problem if you don't ground the generator properly is that an accidental ground placed on the "live" line would go unnoticed, but would leave the neutral at full line voltage.
Moreover, if the neutral and earth terminals on the generator output are bonded together, an accidental ground on the line would also leave all exposed metalwork at line potential.
If you're going to adopt a floating system, then one side of the generator output must not be tied to the frame and to the equipment protective conductors.
To do that properly, you would then need to employ double-pole fusing and switching throughout the rest of the installation.
There would still be no way of detecting a ground-fault on one line unless you installed a PIM.
