Yes, my understanding is they can, but how much is too much depends on the veg and the rabbit.
I think it'd be too much if it upsets their digestion, or stops them eating enough hay / grass? Mine can't have much at all but they've had ongoing issues for a while that make them more sensitive. I know high calcium veg needs to be watched if they have bladder issues too. I guess if they were overweight it would be something to look at and maybe reduce as well.
Thanks for answers. Thought that would be the case with veg. Keep seeing that they should have lots of leafy greens, but it seems that leafy greens (spring greens, cabbage etc) make them gassy! Will stick to herbs and bunny safe branches from the garden I think! Although they are not overweight and don't seem to have any issues with my current regime