Roll20 is system agnostic so any game mechanic, in theory, can be used. You would have to know what dice, if any, are used then you can either use the basic dice engine or create macros for any of your rolls that would be needed. The general roll20 wiki has lots of information to sort through so you will need a clear understanding of what you require roll20 need to do for you to run your game. As you are more familar with the game, you will know better than me or another none DR larper what you need to convert the larp over to a pen and paper game format.