...nevermind, just learned that it only appears if the active render supports it - which is strange, because when i open a tutorial file with a blend material in it, vray rendered it just fine, even though it apparently "doesnt support it"
as an aisde, the work around here was to:
1) disable vray as the active render (set to scanline or whatever...)
2) create the material. seleting Blend from the general list
3) reactivate vray and then apply the VRayMtls to material 1 and 2 and set up the mask
4) render, without issue
that makes for a rather terrible workflow.....