The spare had been mounted inside out, with the letters facing inward. The plate with the stud bolts was 8 on 6.5in whereas my wheels are 8 on 170mm, so I had a hell of a time taking the wheel off of it since it had been forced into the studs.
I took the plate off, banged the plate off of the wheel, repositioned the plate a couple of inches upward (the aluminess tire carrier has multiple bolt positions for the plate with the studs) and jammed the wheel back on (since I don't have the correct 8 x 170mm stud bolt plate).
Bingo, the wheel is high enough so that it doesn't interfere with the reverse sensors!
Still to do: ask SMB to send me the right plate and replace it.
Thing that bugs me is that when I picked up the van, I asked them if they could mount the wheel facing outward, because I thought it would look better. They said "no", it wouldn't fit, so I let it go. As it is, if they had done it right the first time, I wouldn't have had to go through the trouble; not to mention I almost started dicking around with the sensors, when I didn't have to at all.
Here's a picture of how it looks now: