In my view it's impossible to generalise with this, as what will result in a problem for one rabbit won't for another. My rabbits have never had a problem with either greens or herbs, but I know this because I have observed them after eating them. In a similar way it might be that particular greens cause a problem, rather than all. It's probably also fair to say that greens are more likely to cause a problem than herbs. The key thing really is to observe your rabbit for any ill effects with any food and pay regard also to the quantity.
If it's any help I give my now single rabbit a handful of herbs at a time and when I have lots of different types available he gets a mixture.
