Alright. If nobody else wants to answer this one...
> If the cards are marked to check for bj is it possible or likely
> that the shoe is being stacked?
Possible, yes. Likely, no.
It would be very easy to install an IR sensor that detected the presence or absence of the black mark on the corner of the cards. It would be substantially more difficult to design a shuffle machine that takes advantage of that. I would be quite amazed if any casino would risk using such a gaffed shoe. It would leave far too much evidence if it were ever detected.