For veg, I dont think it will make much difference, if youre using a good HPS bulb, and not 1 that's Not Color corrected with some blue.
If it came down to cheap non color corrected HPS bulb vs Halide. Id use the Halide everytime.
Like I said. I myself use the color corrected Hortilux HPS. Technically Halide may have a better color spectrum for veg.