What line-line voltage is your existing generator?
If it is 400-440V line-line (RMS) at 50Hz then in theory you COULD connect a single phase-neutral (assuming you have an accessible star point) to your single-phase EV charger, giving 230-240V RMS, with approximately 6-7kW (~28A) capacity on a single 230V single-phase outlet. This will operate.
However, this wouldn't be recommended in the longterm since essentially you will be applying 100% negative phase sequence currents to your poor generator, which will result in a power (torque) ripple from 0 to double the EV charger power, 100 times per second (twice the electrical frequency). Its likely you could damage the generator/diesel bearings etc over time. The electrical voltage unbalance will also be non-ideal. But, it may not be a problem for a small generator - you could ask the manufacturer.
It would be much better for you if you could either get a three-phase charger, or, if you could arrange for balanced loads on the three phases. There isn't much point leaving your resistor bank connected since it will just waste energy, and won't reduce the power/torque ripple, you actually need to try and add equal loads on the other two phases (ideally at the same power factor) to match the existing single phase load.
Dr. Andrew Roscoehttp://personal.strath.ac.uk/andrew.j.roscoe