IBM changed their entire (almost) lineup of X-series servers. It seems that most of the SCSI/SAS variants now have ServeRAID/Adaptec chips, which makes them unusable on OpenBSD. X3455, oddly, has an LSI1064 SAS and should work fine.
Just to correct myself. x3200 and x3250 (both available with either Penitum D and XEON) also come with LSI1064e SAS/SATA controllers. The rest of boxes have either Adaptec AIC-9580W or AIC-9410. All the gory details at http://www-03.ibm.com/servers/eserver/education/cust/xseries/xref/usxref.pdf
