In all honesty I'm more a chapatti/naan man so don't go for rice dishes, so have never experienced the veg curry that accompanies a biryani, but for what it's worth I've never seen any of the BIR chefs in my locality prepare their veg curries like that. Like the meat the veg is pre-cooked (some places from frozen) and added to the pan in the same way.
But maybe some places have a huge pot of base with veggies in it, just for this very purpose?
I guess it's just different ways of achieving the same end result. As long as it tastes good!