Chit pull is easily implemented using a deck. However, in a physical game, chits are (typically) drawn blind. So a problem arises when chits have different backs, because the player drawing a chit can see the type of chit and - unbeknownst to other players - may cancel the draw and re-do it.
example: JdG Montmirail & Vauchamps 1814 has this flaw.
Players end up drawing all the chits and rolling an x-sided dice to determine the draw.
The module designer can be extra effort in to implement chit pull in a secure way. However, it would be easier for the designer to avoid this problem if Vassal allowed a masking image to be specified at deck level that would be super-imposed on any card mask.
A less efficient method would be to allow a layer to be specified for the card mask itself.