Im thinking about installing a floodlight to my familys summer house as a yardlight. Electricity is generated by either Engine-generator or inverter so no "pure" electricity is avaiable. Ive been thinking about MH floodlight but how stable electricity it requires? Should I use MV lamp instead? I have couple SBMV lamps installed in woodshed and those are little too picky about the electricity. every time I start coffeemaker or other high wattage appliance its pretty sure that one or both SBMV lamps gonna shutdown. I would like to use MH lamp but will rought electricity kill it prematurely? 

I think only option would be using wide input voltage range (120..280VAC 40..70Hz input rated) electronic ballasts, mainly with the genset, if the light would not be the only load.
The reason is quite poor dynamic response of the voltage and frequency regulation of the generator set, mainly on changing load (turning ON the cofee maker,...).
If the HID lighting system is the only load and it is turned ON/OFF by starting/shutting down the generator, there would be no issue at all, as there would be no changes on the generator load.

If you have an inverter from the battery, this would behave way better, unless you overload it (even brief overload cause voltage dip extinguishing HID's).
I think the best would be using separate inverter for HID's only and in parallel feed batteries from the charger (constant 14V for 6-cell "12V" wet lead-acid battery, 13.5V for SLA, current limit for both at about 1CA) supplied from the generator. If the voltage from the generator would fluctuate now, the battery would cover dips and overshoots, so they will not reach the HID system and cause troubles there