It works!

Before just tearing the drive out of there, I manually selected the unit as "F--faulty" in the s/w raid manager. This caused the raid to become degraded. Then, I selected the unit as "R--hot remove". After this, I physically removed it. Nothing bad happened! Throughout this whole process, I had been playing a long audio file stored on an iscsi volume on this raid array. I did a unit rescan and found that, indeed, the drive was no longer there, but the other two were still there, and the array was fine. It was just degraded but still clean.

Then, I put the drive back in the slot and did a unit rescan. It showed up as "available"! So, I added it as a spare for MD0, which was in a degraded state. It immediately started rebuilding. Rebuilding is faster than initially building, for some reason (50MB/s vs. 20-40MB/s).

So, I'm still listening to the same audio file that I was at the beginning at this process without any hiccups or errors.

Tomorrow, I'm going to just remove the drive immediately without warning the software. We'll see how that goes!!!