Found in the spares config guide at http://www.intel.com/support/motherboards/server/s5500bc/sb/CS-030216.htm:
"Intel® Remote Management Module 3
Note: Compatible in SC5650DP/BRP chassis and
system SC5650BCDP. Not supported in the Intel®
Server System SR1630BC due to physical space
Thank you, I had located that note...
*If* you're willing to sacrifice the (only) expansion slot (which I am on a couple of these machines) then it can indeed fit -- I've done a chop-job on the adapter plate from one of the units I had installed in another machine, and have it (ugly) fitting in one of my servers without issue.
The plate which comes with the unit is a full height "backwards" plate from what would be necessary to fit in the SR1630... so If Intel wants to make a half-height plate, this would still be usable in the SR1630BC...