Just looking at the configs is not enough of what to expect for oregen. We will do diamonds as an example.
By default, vanilla generates one cluster of diamond or per chunk, right? Wrong. It ATTEMPTS to generate one cluster per chunk. When, I believe it's, iWorldDecorator is called it chooses a single location (because diamond on makes 1 attempt) and attempts to generate the cluster. Now, to my understanding, it will only replace stone. So if the location it chooses is under Y5, it won't replace the bedrock so you loose some of those diamonds.
Now I'm not sure of the order it happens, but gravel and dirt are randomly populated the same way and replace stone. If diamond is populated after them, it won't replace them. I assume they are populated first since I've never found ores in the center of them.
Now, if I understand correctly, lava, water, and caves do a destructive replacement when populated. This means any block in the area selected for them is replaced with lava source, water source, or air.
This means, yes, potentially you can be the luckiest person in Minecraftia and mine a 9x9 chunk and find 81 full 8 diamond clusters, or be the unluckiest and have the decorator prevent/destroy every diamond ore. Both are a bit extreme, and though highly improbable, not impossible.