Unfortunately that's not it. Even after using dd to wipe the partition table, some information about the zpool persists, and I think that's the issue. When I try and add my disks to the zpool, it gives me a warning that they might already be in a zpool, so I know that something isn't getting wiped properly. I can force it to add the disks and complete the installation procedure, but I still end up with an unbootable disk.
I chose freebsd because of the data integrity mechanisms in ZFS, but it seems to me that there are quite a few issues to be worked out. Maybe the safest thing for my data would be to go with debian or something for now and wait until ZFS is better supported on freebsd.