Here is a flickr set of my (since sold) XCeed Color 30HR, which looks like the one in question. Micron bought Xceed at some point, it looks like.
JDW, if I'm remembering correctly, Micron/Xceed made a bunch of SE/30 video cards, only some of which could use the greyscale adapter, and the thing to look for is the second multiprong connector on the card. See the white 10-pin connector on the bottom center of the card? (Second photo) That's what the greyscale adapter attaches to. The black one to its right connects the external video plug which replaces the knock-out at the back of the computer. If the card doesn't have the white one, it is external video only.
Sadly, that SE/30's capacitors died right after I took the screenshots above, and I haven't had time to fix it yet. Though I just had to replace the faulty capacitors in my iMac G5
so I'm in practice now, at least