Piezography is not just Jon's name for using multiple gray inks to break up the tonal scale, but also the shape of the overlapping inks and the way final linearization is done. Using a single "black only" channel of one of his inks does not make a piezography print, it makes something that goes completely against the very idea of Piezography. Using 4, 6, or 7 shades of Cone inks and profiling with QTR does not make it Piezography print either, since the shape of the curves is as much of what makes a piezogrpahy print as the inks used. All those things make them piezoelectric inkjet prints, but so is using the epson ultrachome inks and driver.
To answer your other question about MIS and Cone shade 1 inks compatible. The short answer is no, they are not. The MIS inks tend to reach their dmax sooner and then level off, someplace round the 30%-40% mark, and the Cone inks are between 35-50% and then start to reverse fairly quickly after the dmax is reached—in most cases shade 2 at 100% might end up being darker than shade 1 at 100%. The other difference is the shape if the density increase between the two inks is different as well, so your black only curves will now be correct if you switch to the Cone Shade 1.
Not knowing the gallery or what your prints are like, it is hard to know what they are trying to get at requesting "piezography" prints—they might just want to make sure you are making pure carbon prints without using color inks.
Richard Boutwell