I believe setting that value to 0 would eliminate the SPARES_LOW warning, but the real question here should be "should I have zero hot spares available?", to which my answer would be no...Now if you have cold spares on site, that would make me less nervous, but I'd much rather see a hot spare be available.
EDIT: Just tried this and go the following:
option raid.min_spare_count: Cannot be set to 0 if there are more than 16 drives or any RAID4 groups configured.
The system has 8 disk and partioned with root-data-data. They are provisioned into aggregates such that each controller uses 7 data partitions for filesystem data, and one data partition remains as a spare. (Recommended during installation)
So there are no spare disk only a spare partition per controller.
I just confirmed in Fusion that the partitioning you described is as expected from ADP R-D-D. Because of this, you should be able to adjust MIN_SPARES to 0, I didn't have access to an 8 drive system, so I was unable. As you can see in the error message from my previous reply was that setting it to 0 on systems with more than 16 drives isn't supported, but you are well under that threshold.