clarkwinkelmann Of course the specifics of the implementation is up to the imagination of the developer, but in the case of RPoL, it is something like this:
Under a menu accessible from the top, you select the XdY (X being the amount of dice, Y being the sides of dice) to throw, optionally counting methods and some other functions, and finally a reason for why you made the roll. The results are all displayed in a list that can be viewed by players unless the rolls were made secret.
It's a pretty advanced roller, so having an inline roller in Flarum posts as you suggested would serve the same purpose. Ultimately all that is necessary is just having the results be visible to users for the sake of legitimacy.