You say 208V, but what is that referenced to? Remember that
voltage is not an absolute value, it is always compared to something. You also don't mention what kind of
power the
dimmer pack requires. For instance, the
dimmer packs I used in high school required three
phase/five
wire 120/208V
power.
As far as that "208V" generator - my guess is that the 208V you specify is between hots - that is, the generator generates three phases of AC, each of which measure a
voltage of 120V to
ground and 208V from hot to hot. Chances are, it will work fine for you, as long as it provides outlets that are 120V to
ground, as well as 208V hot-to-hot.
If there is any doubt, ask the rental
house to tell you exactly what kind of
power the
dimmer pack requires, and what kind of
power the generator provides. If they don't match, tell them to get you something that does match.