The plugin you linked is for a different forum engine. With the limitations you have with vbulletin plugins and the way it handles custom bb codes, I don't think it will be possible to implement without rewriting parts of vbulletin itself. So you'd more or less have to reinvent the wheel just to add this dice rolling thing.

As nifty as it would be to have a dice rolling system, there's no effective way to implement it with all the features you have described. Especially if you want to catch "cheaters". I don't imagine any staff would be particularly keen on moderating dice rolls.