in defense of my example of small diesel driven alternator,
i was not in reference to a hand crank 20 hp diesel at sub freezing temps, for that yes it is a hand full and then some, rather
i was suggesting a smaller electric start diesel in the sub 10 hp class, and i would assume a moderately insulated enclosure, without auto start capability.
for colder temps i would incorporate a glow plug in the intake to aid in starting, or retrofit a starting aid (ether) injector.
the small chinese diesels are high compression units, that shouldnt be that bad to start even in very cold climates.
i have personally started 1693 cat's (probably the most difficult truck engine to start) at -20 degree's F , when everything including the fuel has either frozed or gelled. it takes a bit of work but can be done, these were truck engines setting outside in the wind.
also i might add, small gas engines are a bear to start in sub zero temps too. especially if the thing has not been started in a long time and has condensation in the fuel (ice).
as far as using the inverters to recharge the battery bank thru the use of a 120 volt genset, yes it can be done and very well controlled, but..
if the battery bank is large and below 50%DOD, you better have a large charging capability or you will be running the genset for a very long time.
with the marine alternator controllers, very large charging currents are directed to the battery bank to get from very low capacity to 80% SOC, (temp compensated of course), after which the charge rate is tapered back. Essentially doing the same job the inverter charger does, but also they are programmable.
perhaps your inverter charging capability can deliver 1.5 to 3 kwatt at 28 volts, if so maybe you would be better served using the 120 ac genset
also dont forget that you will also need to have somesort of disconnect if you plan on feeding your loads direct from the genset, this will add to the cost and complexity.
there are many variables envolved in this question, and clearly there is "one solution" to fit all circumstances.
bob g