As Jonathan noted, the VDatum correction input file needs to be in the same format as other input files for SLAMM. SLAMM then reads in the correction values from the raster on a cell-by-cell basis according to equation one in Dean's post.
You must then convert this into a raster using some sort of processing techniquie but we do not currently support this process.
You must then convert this into a raster using some sort of processing techniquie but we do not currently support this process.