Softraid for RAID 1 is
not ready for production use. It cannot recover from a failure, nor continue in degraded mode (single drive) in the event of an outage.
If you wish a software RAID 1, use RAIDframe until softraid development for RAID 1 completes.
As to when ... my guess would be OpenBSD 4.5+; 4.4 may get a functioning RAID 0 and CRYPTO only.
viz:
http://marc.info/?l=openbsd-misc&m=121574753906319&w=2