For what it's worth, I was able to get my M1015 working on FreeBSD 8.2 using the driver from LSI's website. I hammered it for a while (ZFS scrub in background, while simultaneously rsync'ing a bunch of stuff over from my main server) and it seemed pretty stable and pleasantly fast. Unfortunately the driver install process is rather a pain, requiring a kernel recompile, which can take hours if you have to rebuild world.
The biggest problem was that I couldn't get SMART data out of the connected drives. I'm not sure if this is a driver problem or due to FreeBSDs implementation of smartctl. I also had one incident where the server hung on shutdown and wouldn't power off. I'm not sure if that was related to this card or not.
So overall I would say not an ideal choice for FreeBSD, but it can be made to work. Needs more stability testing though.